It depends what you mean ..trying not to assume too much..I take it you want to put an acoustic through an amp. If so you will need a pickup..I know nothing about these...except that they're called peizos. You can also get (usually) single coil pickups (resemble Strat/Tele) which go in your sound hole.I don't know much about the sound of those either.

Tell us more and someone will probably be able to help you. In the mean time go to http://www.harmony-central.com/Guitar/Data3/ and have a look at what is available