A couple days ago I posted a few general tips to get folks started in SC2 multi-player. Today I will go over a few tips that are specific to playing the Terrans.
Wings of Liberty's single player experience focuses primarily on the Terrans. There will likely be some sort of tutorial to explain the ins and outs of the Terrans, which makes them an excellent race to start out with if you're new to StarCraft multi-player.
Terran Tip #1: SCV's and Repair
The Terran's worker units, the SCVs, can repair buildings and mechanical units... like they could in the original StarCraft. New to SC2 however, this repair now has an "auto-cast" feature, much like the Priest's "heal" spell from WarCraft III. Simply right-click on the "Repair" icon and it will enable the SCV to repair anything within range... assuming you have the resources to do so.
This takes some of the micro-management out of Terran base defense, and recovery. Now, when you bring a half-dead group of Vikings back to base after an attack, you no longer have tell an SCV to repair each Viking in your army. They'll keep themselves busy doing it for you, so you can focus on other things.
Terran Tip #2: Using buildings as a defensive "wall"
Many of the Terrans' primary means of base defense rely on killing enemies at range... before they can get too close.
One very effective way of forcing ground forces to stay at range for the Terrans has always been by blocking off ramps, or choke-points with buildings. In SC2, this is still an extremely useful strategy. The Terran Supply Depots even support this strategy by having the new feature of being able to submerge underground and allowing units to walk over them (as to not trap your own units). When an enemy attack is incoming, you can tell the Depots to pop back up and block the way.
If you're going to utilize this strategy, there is one thing to remember about the grid-map system that all SC2 maps use: Many ramps will not be fully blocked by Supply Depots alone... but they can be used to limit the number of melee units that can attack your defense at a time. Considering both Zerg and Protoss have melee Tier 1 units, it makes this a very effective early ground rush defense.
Terran Tip #3: Detectors
The Terran mobile detection unit (detect means the ability to see cloaked or burrowed units) is the Raven. Ravens have many other abilities other than detection, but they are slow moving, easy to kill... and expensive.
Now, I'm not saying the Raven is a bad unit... they're my favorite new Terran Unit... I'm saying that they make lousy detectors. Unfortunately, Detection is essential for the battlefield, especially later on the in the game. Fortunately, Terrans have other means of Detecting aside from the Raven.
Terran Command Centers can be upgraded to the Orbital Command Station which allows you to scan an area of the map. This is an excellent way to scout, but it also detects any units within the area scanned for a short duration. My tip is to have the Orbital Command hotkeyed, so you can use the scan quickly during an attack/defense.