How do you replace the CD player in a car?
Second is to get the appropriate wiring harness for your car. The basic wires for a standard 4 speaker system is a power wire, a ground wire, a remote wire (which turns the unit on and off when it's supposed to) and your speaker wires. the speaker wires are easy to determine because there will be 2 wires of simillar colors... like purple and purble with a black stripe. one would go the the + side of the speaker and one would go to the - side. there should be 8 speaker wires all together, 2 per speaker. there is a big plug that installs in the rear of the head unit, it is generally black. this is the antenna wire, without it, the unit won't even operate at all.
There are many different types of cars and car stereo systems with many different factors. Just play around and you'll figure it out. Remember, you can always call a car stereo intallation place for free information.