your new stereo should have a wiring chart in the manual. It should say Front left speaker, 12V+, ground, etc... or the wires should have stickers on them with those labels.
Match up all the wires from your OLD stereo to the new one. Left front speaker goes to left front, etc.
if you need to, Google search your stereo to find wire charts. most manufacturers have online manuals somewhere.
it should be an easy matching game, and most colours are common for each wire's function. some may be different from one manufacturer to another, so just double-check, and wire things up with your battery disconnected so you dont shock yourself or your new deck.