Decide on what sub(s) you want first, then match an amp to it by figuring out the optimal power at the given impedance of your sub(s). Then to hook the amp up, you will need to run the power wire to the battery, with a fuse on it no further away than 18" from the battery. Ground the amp to the vechile somewhere using as short of a cable as possible, and keep the ground wire the same guage as the power wire. What guage power/ground wire you used is determined by how many watts your amp is, and/or if you are running multiple amps. You will also need a remote wire that is generally connected to the headunit, but can also be wired to some other 12 volt source, that turns the amp on and off with the car. It's best to wire it to the headunit so that the amp turns on and off with the headunit. You will also have to eitiher run RCA cables from the headunit which is the most desired method of connection, but if you are using a factory radio, you may need to get a line output converter to convert the high level aka speaker level inputs to RCA inputs.
