The standard home theater setup consists of five to seven speakers and a subwoofer. The center channel speaker anchors the sound to the picture, and provides most of the dialogue and much of the special effects. The front left and right speakers deliver a wide soundstage, and work with your center channel speaker to reproduce on-screen action that moves to the left and the right, giving you a more realistic and exciting movie experience. The front speakers also act as the left and right stereo speakers when you listen to music.
For more info, check out our article on choosing speakers for home theater.