Yes you need a GPS, a TNC (terminal node controller) and a radio. The GPS sends your location data to the TNC, the TNC encodes it and sends it over the air to a digipeater. A digipeater is a repeater that is connected to the Internet and is able to receive the digital signal and send it to a site like find-u.com or UIview.com. The location of the transmitting station shows up on a map.
APRS can also be done simplex where the TNC is connected to a computers sound card and the data is decoded and overlaid on mapping software.
Some radios can be purchased with a built in TNC so all you have to do is connect a GPS. Icom now has a rig with a built in TNC and GPS.