Part 1: Terran Infantry Units

Bunkers: Bunkers are nearly essential for an early Terran build-up. Bunkers protect from Psi Storm, Broodling, and Irradiate. Use bunkers early on to counter early offensive maneuvers better than any other race can. Use bunkers to protect Ghosts and SCVs on the front lines. Don't forget to repair bunkers as they are being attacked. Use bunkers to protect from air and Mutalisks especially: marines inside do normal (full) damage to Mutalisks (Zerg flyer who takes half damage from Goliath, Turret, and Wraith Missles) and Mutalisks cannot easily kill the high hitpoints of the bunkers. Marines and should be the main inhabitants of bunkers, with the occasional Firebat. Having men in bunkers also hides what type of infantry you are producing, so it's good to hide ghosts in them. Sometimes you can be sneaky and have only 1 or 2 men in a bunker; it will still act to keep enemies away since they'll expect it to be full.

SCVs: Believe it or not, these little guys can be your most powerful attacking weapon. Their ability to build towers (missle turrets) and bunkers and repairing units and structures will aid tremendously in your attacks. Protect them always when using them in this manner. A good way to protect them is to stick them in bunkers. SCVs can be used to kill spider mines without setting the mines off. The first units the enemy should kill from your attack force is your SCVs.

Marines: Marines are cheap and easily killed, but they can kick tons of butt! They are great for taking out other race's towers; the towers attack slowly and can only hit 1 marine at a time, plus the range of Marines gets them quickly into killing range of the towers. Marines do normal (full) damage to air and ground, so are very useful in any situation. With stimpack, they can do huge damage! (keep in mind stimpack usage takes 10 hit points away, so use it when your men are likely to die and you want them to get maximum hurt on the enemy). I recommend researching range for these guys rather early on. I research stimpacks in games where marines are doing a lot of rushing in without the cover of bunkers. Marines are small and can fit through tiny spaces. Always remember to build extra barracks when you have excess minerals. Early on Marines should beware of Spider Mines, Guardians, lots of Hydralisks, lots of Zealots, Psi Storm, and Reavers. Later on, Archons, Ultralisks, carriers, and guardians are good marine killers.

Firebats: Firebats are good for killing Zerglings and Zealots; you will need lots to kill zealots though (same number of at least). 'Bats are also great to drop off in the peon resource line to kill peons quick (bats do splash damage which means they hit several guys at once). Bats can't hurt friendly troops unlike Siege Tank shots and infested Marines. A few Firebats in bunkers will annihilate attacking Zealots and Zerglings. Never go nuts building bats since they cost gas. Bats are my least used terran unit. Oh, and as with Marines, with stimpacks they can do unbelievable damage.

Ghosts: Ghosts are one of my favorite Terran units! When you need ghosts, make a lot of them since they die easily and can only Lockdown once or twice. Remember to build ghosts before you research their specials if gas is scanty. Remember, unless you can afford the expensive and slow building battle cruisers, ghosts are your only way to kill Protoss air units well by using Lockdown. Ghosts can be put in bunkers for protection. The biggest enemy of a ghost is the Protoss Observer. Try to have towers near your ghosts to spot the Observers. Placing defensive matrix on a ghost is a good idea if he needs protection. Keep "casting" matrix on him till his job is done. Remember, a ghost is primarily a support unit.

Ghost Special Abilities

• Cloak: Ghosts can cloak to sneak around, which can be useful when dealing with large groups of Carriers or while spying for a friendly Siege Tank. This is great because you can instigate enemy units with your long attack range and sometimes make them run into your defense/trap of mines and Siege Tanks. Always use cloak when nuking. Also, when you get rid of their towers, use cloak to sneak in on enemy Siege Tanks and lock them down so you can move in your forces for the kill! Cloak should be the third thing you research for your ghosts.
• Lockdown: Ghosts with Lockdown are the best counter for Protoss and Terran air units. Remember to have air killers nearby to clean up once you have locked down enemies. Don't forget to use Lockdown on Tanks, Reavers, Dragoons, and other mechanical units. Be careful not to cloak in such a way that it lowers your ability to lockdown when vulnerable enemy air units are approaching. For example, when a ghost has full energy with the energy upgrade, he can only cloak for a few seconds before his ability to lockdown is reduced from 2 lockdowns to 1. Lockdown should be the first thing you research for your ghosts.
• Nuke: If you are able to Lockdown several expensive units, that would be a good time to use a nuke to kill them all quickly. There was one game where I was able to Lockdown something like 8 Carriers, an Arbiter, and a couple Scouts with my army of ghosts; I then proceeded to nuke them all! Nuke also comes in handy when Terrans are sieging your town (use it to make them scatter); when they have a ton of defensive structures (towers) and you want to move in; and when they have a lot of expansions (they'll have to guess where that nuke will be going off). Since you should be cloaked while nuking, watch out for towers and other detectors when nuking - don't waste your nuke! When in doubt, save the nuke for later. Try not to nuke right where you are fighting without proper cover because it is likely your ghost's laser sight will be spotted and the ghost will be killed. However, if you need to do this (like when defending a big attack), use several ghosts and defensive matrix, so the odds of them guessing which ghost is nuking is slim - and if they do they have to hit through his matrix.
• Energy capacity: Always upgrade the energy capacity of your Ghosts. This should be the second thing you research, right after lockdown. It gives him longer cloak ability and he will be able to use two Lockdowns while cloaked.
• Ocular Implants: This upgrade allows your Ghost to see farther. Definitely get this upgrade if you plan to utilize the nuclear warheads. The extra sight range could be just enough to be clear of your enemy's towers and other cloak-seeing units.