Installing your new car stereo is so simple all you do is take out the old one by just unscrewing all the bolts from the dash if needed and then just pull out the stereo away from the wiring harness.
Just be careful when you are putting in your new hardware it will be very easy to hook up the wiring harness the wrong way especially if you are hard wiring it back together.
You will just want to start out by pulling anything away from the dash that is needed when trying to take out the existing stereo that is in your car and even more when you are installing the new stereo.
Head units are the easiest type of CD player to install in a car. You just get a new hole kit at Wal-Mart or advanced if you do you even need one and then just put it in so the head unit will fit and not be sliding around and pulling out when you hit the brakes. You will also probably need a new wiring harness with it.
After you install the head unit you will have to either hard wire the existing wiring harness if you cannot find one for the make of the car or you will have to buy one from a stereo store. Then you just hook the head unit up to the wiring harness and then mount the ground wire and then you are good to go. It is really that simple after you read what I just said and then try and install a new head unit.
If you really want your speakers to sound good with your new head unit you will want to get a highs and mid amp to go along with your head unit and speakers it will make it sound all the better with a new head unit.
When you want to get into bigger and better things you can go to circuit city or best buy and buy yourself some subwoofers and another amp to power those and hook that up and really be doing it big. It is a little bit harder to install but it is the same thing. The only thing that you do different other then installing the head unit is you just run the RCAs to the head unit and run the live wire from the amp to the battery it is that simple. The other things you just wire the speakers to the amp and mount the ground wire for the amp and you're done. All that simple and takes probably under an hour if you are doing a simple car to trunk installation. Then you just tune your amp to how much wattage you want to put out and you start bumping your subs and it will sound so good inside a trunk especially if you get this stuff called DYNOMAT and put it all in the inside of your trunk nothing will rattle and it will sound so much better.