Strange. I've never known anyone who didn't know how to tap. Well, here's the basics: You have to use your right hand (usually the middle finger) to "tap" the indicated fret. If your left handed, use your left hand. I really do a bad job of explaining it, but if you check out some of the tutorials they have at guitartricks, I'm sure someone will explain it A LOT better than I can.

Oh, and Kirk Hammett is God.