You send a feed from your amp into the talk box. The talk box then sends that sound into a plastic tube that gets attached next to a microphone. By holding the tube in your mouth and moving your mouth as if you were talking, you filter the guitar sound coming through the tube in a natural way. This filtered sound then gets picked up by that microphone and that's basically it.
[Edited by SPL on 08-23-2003 at 04:22 PM]