I'm going to lay down another basic strategy today. It is the simple terran wall and how to put it up effectively. The first thing to do is to build an scv and make sure you mine the minerals. Around 8 food you should send an scv out to the choke point of your base and lay down a supply depot right on the edge. Make sure you always have an scv in your queue so that you can keep mining constantly. A little bit after the depot finishes you should be able to get 150 minerals in which case you should put down a barracks next to your depot.
With these two buildings, you now have a choice. If you are going to go defensive, then it would be in your best interest to wait for the barracks to finish and put a bunker to fill in the last slot. If not, then build another supply depot to close off the hole as soon as you can. This is crucial if you're playing against a zerg player as an early ling rush can easily be fended off with a supply depot wall and one or two marines chipping away at the zerglings. Against another terran or protoss though, the bunker is a safe move to make.
As with any wall, putting stronger buildings will yield a stronger wall, so if the choke is larger such as in a 2v2 or 3v3 map, it would be worth your while to put another barracks or even a factory in your wall. Later on, be sure to add a tank or two for added ground support.