Unlike the 1000s of Starcraft pages out there, I'll assume that you've played Terran before and know the units. I won't have any pictures or information on the costs of units and buildings here. If you're unfamiliar with Terran units, then I suggest that you take a brief look at your Starcraft manuel. My most unfamiliar of the three races is Terran, so I cannot give a good explaination for some of the units.

SCV - These are your workers. You'll need lots and lots of them to gather the necessary minerals and vespine gas to build other units and structures. They can repair buildings and some non-living units.

Marine - Marines are fairly versatile although pretty weak. Since they are your first troops, you should get them early on. If you have bunkers, then your marines can hide in the bunkers and fire at enemy troops within range. The bunker can protect the marines until it is destroyed, leaving the marines unharmed. 12 marines fully upgraded (including stimpack) will be very devestating cuz they're versatile and strong now.

Strong Against : Zerglings, Mutalisks, and Overlords
Weak Against : Zealots, Hydralisks, more advanced units such as Ultralisks and Carriers

Firebat - Firebats are a stronger, souped-up version of the marine, but they cannot attack air units. You should combine them with marines unless you're not afraid of the enemy attacking/defending with air units. They have a much shorter range than marines, so you're better off using these guys on defense.

Strong Against : Zealots and Zerglings
Weak Against : Air Units, Reavers, Ultralisks, Archons, etc.

Ghost - Although ghosts inflict a lot of damage, they have spells that are quite useful. Lockdown is good for large and powerful units such as carriers, battle cruisers, scouts, etc. Cloaking will render then undetectable to many units when you need it for an important task. Nuclear strike is very horrifying to the enemy (to say the least.) You'll need to build a nuke at a nuclear silos, but if you can launch this nuke with a ghost, it'll do like 200+ damage in a large radius!!! The center receives like 750 damage.

Strong Against : Large clusters of buildings, Carriers (lockdown), Scouts (lockdown), Arbiters (lockdown), just about any mechanical unit.
Weak Against : Just about any non-mechanical land unit with detectors nearby.

Vulture - The vulture is a bit stronger than Firebats, but again, they cannot attack air units. They can also implement spider mines into the ground which do a lot of damage if a unit walks over it. Be careful or friendly units will be destroyed or injured by these mines. (I don't think your units will be destroyed, but hey, be careful!!)

Strong Against : Just about any land unit that will possibly run over spider mines.
Weak Against : Air units, Ultralisks, Archons.

Siege Tank - These tanks are very popular among Terran players!! They have a lot of hit points and can do a decent amount of damage. The "siege mode" which you can research will prove to be useful when assulting structures or for defense.

Goliath - Goliaths are fairly strong, versatile, but expensive. A decent army of these might still be worth your investment though. These should be part of your main attacking force later on.

Strong Against : Most air units (esp Mutalisks.)

Weak Against : Reavers, Ultralisks, Guardians.

Wraith - These fliers are well-known for their ability to cloak. Try to cloak when the Wraith's energy is MAXed out. You probably will want the Apollo reactor in the Physics Lab to allow the Wraith to remain cloaked longer.

Strong Against : Anything (as long as no detectors are nearby.)
Weak Against : Spore colonies, missile turrets, photon cannons, scrouges, scouts, battle cruisers.

Dropship - These are simply the Terrans' transports.

Science Vessel - These air units can accumulate energy over time and use that energy for Defensive Matrix, EMP Shockwave, and Irradiate. In addition, they can spot cloaked enemy units. I kinda like EMP Shockwave cuz it can disable certain units' special abilities and shields. This is devestating against the Protoss. Defensive Matrix is important since it forms a very tough but temporary armor on a unit. Use it on ghosts before you send them in for a nuclear strike or use it on a battle cruiser to yamato gun and take down a lone but important building.

Battlecruiser - Battlecruisers are the ultimate air unit for Terrans. The Yamato gun can cause great devestation to anything; one hit and a Protoss photon cannon is GONE.

Strong Against : Small buildings, photon cannons, smaller fliers, most land units.
Weak Against : Massive numbers of scourges or other units except for land units that can't attack air.