You wire in your factory antenna, a power wire, ground wire and possibly a on/off switch. Then you plug in your ipod into the unit via a RCA to stereo jack adapter. There is usually two frequencies you can choose from. When the unit is powered on, it disconnects your antenna and broadcasts your ipod music to the selected frequency. I've sat in stop in go traffic on the highway in the middle of a city listening to my iPod with no static or hiss where a FM transmitter would have failed and has failed on me before. I have tried quite a few FM transmitters before I finally went to a wired one.