Audio Systems: car amplifires, rca outputs, rca plugs

Question
how does an high input plug works on an amp and what does it do

Answer
high input allows you to run the amplifier using the existing car's speakers to run the amplifier.  (that didnt make much sense, sorry)
Without the high level inputs you would either need a converter or you would have to change your cd player to a unit that had RCA outputs to drive the amp.  if you dont want to change the cd player in your car and all you want to do is add an amplifier to run a sub, the high level inputs on the amp connect to the speaker wires in the car for signal instead of needing RCA plugs.
Unfortunatly you get ALOT better sound quailty if you change the cd player and use the RCA jacks instead of the highlevel inputs so there is a drawback.