The Terran race has many special abilities, including the ability to nuke, Spider Mines, Cloaking, Yamato, Siege Tank, and several other really cool abilities. The units are somewhat weak, with the exception of the Battle Cruiser and Siege tank, and cost a lot compared to Zerg. The Terran have many special Defensive tactics, and are set up for defense with the Bunker and Siege Mode. This is often the reason that most Terran players loose, however. If you go too defensive, you can fend off most attacks, but eventually you will die. The best Terran players do not use bunker much at all, but rather use things like Siege Mode and Spider Mines to attack. A great way to look at it is to say "can you ever defend your opponent to death?" Terran are great for range units, but lack no-range. The FireBat is a good unit, but that is one unit that has little life. Terran also have the ability to Cloak, which adds a very interesting twist to the game. The Wraith and Ghost can both Cloak, and it is often difficult to fend off a massed Cloaked Wraith attack. The Ghost can Nuke while Cloaked, which is the ultimate and most deadly weapon in the game. Also, the Spider Mine is a great way to scout and lay waste to massed armies. Overall, the Terran are good for special attacks and defending, but aren't the best choice for mass units (Yeah, mass-Cruisers work:)
Terran are very vulnerable to Plague. This is one of the most dangerous things to the Bunker setup. It drains up to 300 life, and once the building is in red hit zone, it starts draining itself. Terran also have to look out for Templar. Psionic Storm isn't as effective against Terran as it is against Zerg, but it can lay waste to mass Marines or any other unit for that matter just as much.
Terran have many special abilities. Some are only good depending on the game, but others are good under most any situation. Cloaking, for example, is effective most of the time. Wether stopping troop movement, defending, or attacking, it takes the fire away from the Wraith and forces enemies to either try to uncloak the Wraiths or aviod them or just let them eat away. If you are going to produce Battle Cruisers, then you will benifit from yamato a lot. Battle Cruisers usually last a long time, so most have a life-span that lasts long enough to fire at least 3 Yamato blasts. Yamato is great for taking down Turrets or Photon Cannons, and helps reduce the life of Spore Colonies. Yamato also takes the life out of most units, or at least reduces it in half. One of the best weapons of war for the Terran is the Arclite Siege Tank. This powerful mobile artillary weapon has a concusive damage of 30. This is a good attack power, but if you need distance or heavier assaults, you will need Siege Mode. This ability transforms the Arclite Siege Tank into a Long range mass of terror which takes off 75 concusive damage unupgraded. The only drawback is that it is immobile when in Siege Mode, and it can't attack anything that is right in front of it. For attacking Melee units, the Tank Mode is best, but for attacking ranged units or buildings, you will want the heavier fire power of the Siege Mode. Perhaps one of the most money-efficiant upgrades is the Stim Pack. This takes 10 life away, but it increases the movement and attack rate of the Marine and FireBat to nearly double. This is not much of a drawback, however, becuase once your units are out of combat a Medic can heal the damage that was caused to use the Stim Pack (This is only for Brood War).
Marines are the first available military unit, and are also mulit-purpose. In the beginning of the game, they are good for rushing, and with the use of the bunker are good for defending against early rushes. Later on in the game, they are good for support attackers. If you use them to defend Siege Tanks in an attack, they can prevent Zerglings from laying waste to your tanks. They make descent drops from Dropships, especially with the Stim Pack upgrade. They are excelent scouts, and are very useful when set to patrol. The Bunker is a great building, but too many Bunkers will lead to over-defense which will only hurt you.
Bunkers are good in early games to attack as well as defend. If you take an SCV to your enemie's base and build a Bunker right outside thier base, it makes it very hard to stop this attack. This is good against Zerg especially, because they seem to lay victim the most to Bunkers. Build close to the Peon Line, and you will put a very quick stop to enemy economy. This spells certain doom because it stops the production of troops.
Marines are great for defending a Siege Tank. This can make a good drop. Take a Dropship, a Siege Tank, and 4 Marines and find a cliff close to your enemy. Unload, and position the tank so that it can hit something. Tell it to Hold Possition, and then position the Marines so that they make a wall around the tank. This way little Zerglings wont get through and fry your Tank. Tell the Marines to Hold Position, then move the tank into Siege Mode. If you're on a cliff you should do a lot of damage, but if you are not you may not go too far. Nontheless, if you catch them by suprise, then you will ensue chaos apon their army.
FireBats are early game no-range units. They inflict heavy damage, but have little life. This makes them near useless against Hydras and Dragoons as well as Bunkers. But they are excelent for Zealots and Zerglings. If 12 Zealots fight 12 FireBats, All the Zealots will die, and 6 FireBats will live. They are awesome against players that mass Zealots or Hydras, but other than that they aren't very good. They do, however, make good drops and are good also, like the Marine, in defending Siege Tanks in battle. Take a Dropship stuffed full with 8 of these and unload at a Peon Line, and the results are incredible. They are a little expensive to loose though, if your Dropship is shot down. To defend an attacking Siege Tank, follow the same directions as you would with a Marine.
The most synonomous thing with a Ghost is a Nuke, and for a very good reason. Ghosts are not very effective, and are not worth the money they cost if they do not have any of their abilities. The are good for spotting for a Siege Tank, because their sight range can be boosted to be better than a normal unit, and they can cloack and become unseen. They can also use Lock Down, which is a very good weapon. It freezes enemies into a bubble where they can't move but can be shot. It is very good for taking down Battle Cruisers. The Nuke is the best of the Ghost's abilities, because it can inflict 1000 damage and has a heck of a splash damage. The hardest thing is pulling it off. Ghosts are cloakable, which makes them easy to hide. But you have to find a good target, then you have to find a place away from detectors and also have to hope that your enemy does not kill the Ghost before the Nuke falls from the sky. Some good places to put Ghosts are in little cracks or hard to see places, on top of cliffs or behind the protection of Siege tanks. Also, don't always try to Nuke in the center of something. Often if you get too close to your enemies, they might have a Turret nearby that you run into by accident and you would loose the Ghost before the party even begins! Some other tactics are to have multiple Ghosts, just to confuse your enemy, and also Nuking several times at once is a near assurance that one will hit.
Ghosts have the ability to Cloak, but because they are so week this isn't too much of a threat! But they are useful for scouting nontheless. They are good for infiltrating enemy defenses, and once that is done they can Nuke from inside a base, making them hard to find, or they can lock something down, if that would do any good. In a special game, where your enemy has some kind of special character, you can sneak in and lock him down right before you attack, and that character will be unable to assist in defending your attack. In other games, you might have lots of minerals. In this game you can train lots of ghosts, sneak them in, and lockdown a lot of things. It wont do much good, but you can lockdown the Probes or SCVs. Then you can kill them all... But if you can sneak a Ghost in behind enemy lines, you can use a Nuke and no one will expect the Ghost to be inside their own base!
Ghosts are good at attacking small units, taking off 10 damage unupgraded. They aren't very good against large units, they only take 5 off. But they are pretty cheap and very useful, plus they can cloak and lockdown.
Vultures are the first available vehicle, and they are useful in both the early game and mid-game. Early on, they stop Zerglings, Marines and Zealots dead with the support of Firebats and Marines. They are good afterward with their Spider Mines and are always useful for scouting. They do 20 damage to smaller units, but only 10 to large units. This makes them better on smaller units. They are not very good at destroying buildings, so that isn't their purpose in life. Use them in taking out small units like Marines Zerglings and Zealots. Let Tanks or Marines handle the larger units.
In the middle of the game, you should not discontinue your production of Vultures. They are great for speed and scouting and very useful for hit 'n' run attacks. If you have the speed upgrade, you can often whiz by defenses to your enemie's peons and take them out befor they have a chance to stop you. If they kill your Vultures you will probably have lost more money worth of units then they did, but they are further set back because their income has been slowed down. Also, If you get a chance to destroy bunkers, what is left is 4 or less small units. This is your oppertunity to strike with Vultures! They come in and slaughter the remnants of the bunkers with no problem!
Lay mines all over the map. They don't take money to trian, each Vulture has 3 to set. They don't take up Supplies either, and they provide good scouts and as their name suggests, mines. In the middle game, you usually have a lot of extra money to spend, so you can train about 12 Vultures to lay 36 Spider Mines all over the map, and try to use the remaining Vultures to kill some peons, scout your enemy out, or take out other mines. The Vultures are hovering units, and Spider Mines don't attack hover units.
Tanks are often underestimated and left as defense in Siege Mode. But if you use Tanks correctly in Tank Mode, you will find that the use of their Mobility is invaluable. The best way to use these is to mix with other units. Use these along with Marines and Vultures and Goliaths and they are great! They provide long range and heavy firepower even without Siege Mode. The two biggies that make Tank Mode better than Siege Mode are mobility and minimum range. What that means is that Tanks in Tank Mode can attack anything within their range, from 1 matrix away to 6 matrices away. Siege Tanks in Siege Mode can't attack anything within 2 matrices, making them very vulnurable to Zerglings and Zealots. Tanks in Tank Mode provide range and firepower, mobility and are hard to take out. When you attack, they usually stay in the back, so incoming enemy units will take out the other units you have first, leaving the Tanks unharmed. The last reason why you should use Tanks in Tank Mode is because they don't do splash damage and hurt your own units severely.
Siege Mode is better than Tank Mode for 2 main reasons. One, that it has unmatched range. Two, that it has extreme firepower. They are good for defense, but they are equaly good for attacking. They provide hard to reach range, so most units cannot reach them befor dying. This annihilates ground defenses, and this is when you should switch to Tank Mode. Tank Mode will do a lot of damage, and if you have a lot of buildings to take out, you wont have to switch back and forth for mobility. Siege tanks are best put with elevation advantages. They have more safty this way. Many maps have small clifts just above the peon line. If you unload 2 tanks here, you can bring devestating effects to peons, not to mention the chaos and confusion it would cause.
Tank drops are hard to perform, but if pulled off are very good. When you unload them, you will want them in Siege Mode so they can get back in the Dropship quickly for protection. Unload and get a hit from each. This will trigger enemies to attack, so load them immediately back into the Dropship. move it back a little, and perform this untill you kill the defense or find a safe place to put in Siege Mode. You won't do much damage until your tanks are in Siege Mode, so you should try to find a cliff or something quickly.
Goliaths are great support fighters. They have a decsent range, have good mobility, and have heavy attack damage. They are great for air, and good against ground when mixed with other units. Many people ignore Goliaths, but they are one of the best units the Terran have, if used right. They benifit very well from upgrades, both armor and weapons. The best reason why these are good and better than Marines is that they are repairable. You can repair them very quickly with a small group of 2-4 SCVs and prepare them for battle again. Marines die much too quickly, having low armor and not much life. Even with the Medic, they die too fast to most units.
A good mix of units is 3 Tanks, 5 Goliaths, and 4 Vultures. The Vultures will take most of the earlier hits, and once again the Tanks will be somewhat protected. Keep all 12 units selected, and have 2-4 SCVs outside the battle area. When you see one get damaged badly, send him out to be repaired. He will be repaired very fastly and be ready to attack immidiately. The only drawback is that it takes a lot of minerals. This shouldn't be much of a problem though.
Wraiths are the first available air unit for the Terran. They are not very strong, but they are very good because they can cloak. They are very vulnerable to EMP shockwave, which takes their energy away causing them to uncloak, and to Psionic Storm, which drians thier life fast. They should serve as support fighters. At first in conjunction with Goliaths and Marines, and when you can with Battle Cruisers. Terran have 3 fighting air units including the Valkerie. So you should send Science vessels to support and help them, and DropShips to unload more units to do more damage.
One of the good things about wriaths is that they are able to be repaired. If you can afford 24 of them, you can deal some major damage out. Havin 4 SCVs will give them much increased life. Select 12 of the 24 Wriaths and make them group one. (hold ctrl down and press 1, to select the group just press one) Make another group with the other 12. Cloak group one and send them in. WIth these aim to kill the detectors. Their life should go down shortly if your target is well defended, so as soon as you see one get mostly red pull them out. Uncloak when you are at a safe distance, and set your SCVs to repair all the hurt ones with waypoints. (Waypoints are issued by holding shift and telling a unit to move. He will finish out his current command then do what you told him to do next.) Meanwhile, take your second group and cloak them. Attack the detectors and try to finish them off, and when you see the first ones start to get hurt badly send them out to be repaired. By the time this happens your other Wraiths should be nearly repaired, and send them in as soon as they are. Keep this patern going. When the detecors are dead, aim for the units. Don't go for the peons just yet, try to hit the larger units like Battle Cruisers or Carriers. You may need to take along a Science Vessel so it can uncloak other units. Also, it can Iradiate Overlords and other units, use EMP to stop sheilds or drain Engergy immidiately to 1 (causing Wraiths to uncloak) or cast Defensive Matrix to add 250 extra sheilds. This uncloaks the Wraith so be careful when you use it.
Dropships are used to load and unload friendly units onto the battle field or just over large areas. They have no defense against any unit, but they have the ability to have very strong armor and are great with support fighters like Wraiths. If you plan for battle, you should load some Infantry into these and bring them along with your fleet. When you begin combat you can unload them to add more power. They are key units to have a successful base and colony on a large air based map or even on a ground based map. Marine Drops are a useful stratagie with these. You can unload 8 Marines with one Dropship. The hardest part is to sneak to the peon line without getting shot down. Once all 8 Marines have been delivered, you should have enough time to take out peons. If you value your Marines a whole lot and would like to keep them, you should load them back in and haul them away. Otherwise you should continue climbing the tech tree and devise another attack. If you think you could make 3 Dropships in to the peon line of your enemy, then you will have enough firepower to take out the Nexus/Hatcherie/Command Center and still take on the army your enemy sends to stop you. The only problem is that if the Dropships get shot down you have a lot of money wasted.
Battle Cruisers are the best units in the game. They have high armor, heavy firepower, lots of life and dispite thier cost and Supply demand they are very good in numbers. Like most units, you should mix in several types. Wraiths for support fighting, Dropships to deliver more units, and Science Vessels to help uncloak or whatever you need them for. Battle Cruisers not only have a powerful Laser Battery, but when given enough energy a long range weapon called Yamato capable of delivering 200+ damage. That is enough to take out most other units, and capable of destroying Turrets or Photon Cannons in one blast. This ability should be researched and used very often to agrivate your enemy and to keep his defenses down to a minimum. Battle Cruisers have a lot of life, and very strong armor. With a Sciense vessel, you can use Defensive Matrix to give Battle Cruisers 250 extra shields. This goes away shortly, and disapears once it has been worn out. But it is easy to replace, requiring only an additional 100 energy. A single Battle Cruiser, a Science Vessel, and a couple SCVs can deal a lot of damage if set up right and executed properly. Just be sure you send your BC out for repairs befor he dies.
For Zerg and Protoss the Drones and Probes are not much use other than to collect resources and build buildings. SCVs are unique in that they can repair damage quickly to any mechanical unit. Whenever you attack you should send 2-4 SCVs along, depending on your attack force, and just those SCVs can make a severely damaged unit become a undamaged again and ready for battle. Also they are capable of building a Barracks or Factory or Starport or any structure almost anywhere, where other races must build near a Pylon or on creep.