If you have two spokes loose, your wheel is probably noticably out of true. Give it a spin and see if it wobbles back and forth. After you do this, give the spokes a squeeze with your hands and see if any others seem noticably loose. They should feel pretty tight. Just a tiny amount of bend to them.

Take your spoke wrench and tighten those two spokes (and any others you find that are loose). It really isn't hard. Try to get them to the same tightness as the rest of your spokes. You can gauge tension by squeezing the spokes or by tapping on them a screw driver (or something similar) and comparing the pitch they give off. The pitch should be similar.

After you get them close to the same pitch, give the wheel a spin and see if it still wobbles. If it does, work on it a bit more. Truing is pretty straight forward if you take your time. If you mess it up, take it to the LBS. It's pretty hard to completely ***up a wheel when your truing it. Have fun!