If you are asking these types of questions, you should really learn as much as you can about car audio before messing around with it. An improper installation could:

1. sound very bad
2. cause damage to your equipment
3. start an electrical fire (I've seen it happen before)

I would suggest reading up at caraudioforum (dot) com and similar sites. If you're still feeling a bit lost, the best thing to do is have a professional or someone knowledgeable in this area do the work for you.