There are a few things you need to know before you can safely go forward and design and build a car audio system for yourself. These are also good tools to have for regular discussions about car audio in general. Do yourself a favour and read, and understand these topics before you start buying things, and definitely have a good grasp in them before you start installing anything.

Electron Flow and the Pump and water example
Series wiring
Parallel Wiring

Combining wiring schemes

Power distribution fundamentals
High-End speaker wire