SCV...
 

                                                                       The SCV is your work force that collects Ore and Gas though it can do
                            much more than just collect Ore and Gas. It can repair burning
                            buildings and mechanical units like Vultures, Goliaths, Tanks,
                            other SCV's, Wraiths, Science Vessels, and Battle Cruisers.  The
                            SCV can also be use of a scouting unit during the game to see how
                            far the enemy has built his building, but only do this in very
                            begining of game.  Cost: 50 Ore

                            The marine is the most cheapest tactical unit in the Terrans force,
                            great for rushing in multiplayer games.  The marine is a unit that
                            is great in large numbers (like a couple groups of 12). The     
                            advantage of the Marine is the Bunker, if you have a full bunker (4)
                            you can destroy expensive units like Mutalisks, Wraiths, Ultralisks,
                            and Scouts. Cost: 50 Ore  

  FIREBAT... 
 

                            The Firebat is another cheap tactical unit that has a short fire
                            range but, devastating fire power and is great for hand to hand
                            combat with ground units like Zealots, zerglings, Dragoons, Hydra-
                            lisks, and Ultralisks.  The Firebat should always be accomponied with
                                                                      Marines in case of encounters with air units.  The Fire bat is a good
                            unit for destroying buildings and can destroy a base with a couple
                            groups of 12.  Cost: 50 Ore 25 Gas 

                    The Ghost is a Cloakable unit that has many uses.  The Ghost can Cloak
                            its self and walk into enemy base to scout out area, but the Ghost can
                            be seen by Missle Turrets, Science Vessels, Spore Colonies, Creep
                            Colonies, Overlords, Photon Cannons and Observers.  The greatest
                            advantage of the Ghost is that it may not have a good attack power
                            but can destroy large amount of area with the almighty NUKE. The
                            Ghost can also use Lockdown on Mechanical units, it freezes the unit
                            inplace for a certain amount of time which gives you a chance to
                            the unit or run away. Cost: 25 Ore 75 Gas

GOLIATH...