That's for the beginning, let's see what we have:
Probably the most commonly played race by new players. But do you know what potential Terran race has in it's abilities? Probably not, or not all of them, but that's why you are reading this now. So let me show you what I am talking about!
Siege mode: The reason I included this here, because you have to pay attention when you want to use this, and click the icon (or hit the hot key) to do so. This ability is a very powerful addition to your army any time. Just click the siege mode icon, wait 4 secs, and nuke your enemies army from a nice distance. See the graph for a contraction between normal and siege mode range. You may only want to leave your tank as is, if you are fighting against heavily armored units, because it does a lot of damage against them in normal mode.See the image for a reference.
250mm Strike Cannons: A very brutal ability, but it needs research and you have to wait until 150 energy regenerates for it to use. You can kill nearly any unit with this, it only need a little bit of micro, to target the right target. Good to use against Colossus or Ultralisk, but you can snipe casters with it, or anything. It deals damage and stuns the target, and it can be used against buildings as well. This makes it very nice to use your Thor with a Medivac, pick it up, go to the enemy base, and snipe tech buildings, or economy buildings (Supply, pylon, queen).
Being a caster-only unit, Raven is mainly trained for mobile detection to go with your army. But it still has nice abilities, which you can use to your advantage.
Build Auto-Turret: It spawns a turret for 240 seconds. Nice to have for map control, or you can harass a mineral line with them, if you can get behind a base, but Raven being a costy unit, it's not really good to use it for harassing.
Point Defense Drone: A really nice ability, if you are facing a massive ranged army. This little drone absorbs ranged shots for a while. Place it as soon as possible, or if you know what's coming, you can place it before the encounter. Try to stay in it's range to get the best result. It's energy pool depletes quickly, but still, it's nice to have a little mobile disable unit with your army.
Seeker Missle: A good ability if the enemy wants to beat you in numbers. The Raven fires a missle, that chases it's target and does Area of Effect damage when hits. You can take out a group of hydralisks, zealots, mutalisks, etc with a well placed shot. However, your enemy can save it's units with a good micro, drawing away the targeted unit.
A little evil in the terran army. Being able to cloak, it can be a little surprise to your opponent. This unit has the strongest skill in the whole game, the Nuklear Missle, but you have to place it well. Ghosts are mainly used against Protoss opponents, because they can lower or take out protoss shields with their ability, EMP strike.
Cloak: It's nice to be invisible. It's even better, when you call down a nuke while you are invisible. This is one of the most important ability of your ghost, but it should be used wisely. Don't forget to turn it off, when you are out of enemy sight.
Tactical Nuke Strike: Do you think it's OP to take out a whole mineral line in 20 seconds? Well, you can do that with your ghost, if you research a Nuklear Missle in your Ghost academy, for only 100 minerals and gas. Whenever you go and use nuke, try to hide your Ghost Academy from enemy sight, so they won't be prepared against your cloaked special ops.
Sniper Round: It's an ability what you can use as soon as your Ghost comes out of your Barracks. I think it's really designed against Protoss, because you can take out a High Templar with a well placed Sniper Round. It only needs goodMicroto do so. But can be used against mineral line units as well.
EMP Round: A very useful ability, because it doesn't need to be researched, and can be casted instantly when you research Ghost's energy upgrade. It does 100 damage to enemy (Protoss) units, and drains all energy from the units in the same time. Don't try it on yourself, it drains your energy as well. Good to use against enemy caster units, and all protoss units and buildings. A real must have in TvP matches.
A really nice addition to your army. But it needs wise micro, if you want to use it efficiently. It can only hit air, when in air mode, and can only hit land units, when landed. You have to be prepared before an encounter, and place them as needed. See the image for a contrast between air and ground mode's weapons. The transformation takes 3 secs.
One of your best friends in the Terran army. Packed with auto heal, and being able to transport units, it's a must have, it you go massive Marine&Marauder army. Your units can use Stimpack more often, getting speed and attack speed.
Heal: It's ability is on auto-cast, when the unit spawns. Heals friendly biological targets, 3 hitpoints for 1 energy. You really don't have to bother with this ability, as it does it's job.
Cloak: Banshee's cloak has to be researched in an attached Tech Lab to the Starport. It renders your unit invisible for a period of time (based on yor energy). A nice-to-have cheese ability, if you can hide your Starport, pump out some Banshees and cloak them, you can cause great loss at your enemy's base.
Stimpack: Your low-tech units can have a nice ability when researched. Stimpack allows you to inject your bio units with drugs, making their move- and attack speed faster for a few seconds. An icon indicates the stimpacked state of your units. This ability uses you unit's healt, so use it wisely, or with Medivac support.
Yamato Cannon: A rarely used ability, because players don't tend to get bc-s. It's a really high-tech unit, and costs a lot. But it's ability, the Yamato Cannon can cause 300 damage to a single unit or structure. Use it when you have enough energy.
These are the abilities you can use as a commander of a Terran army. Feel free to post comments below. The next article is going to analyse the Zerg swarm's castables.