Watch the Left-Hand Muting online guitar lesson by Stu Hamm from Stu Hamm U: Slap Bass

Early in the text I brought up that you are going to have to devise a way to keep the strings that you are not playing from ringing.

This exercise is going to give you a few tips on how you might achieve that goal. There are different techniques that you need to learn to use when you are playing open strings (keeping the other strings form ringing with your left hand) and when you are fretting notes.

Good luck!