There are several different ways to listen music from your iPod in your car.
Cassette Adapter if you have a cassette player in your car then this is probably the cheapest way to listen to music in your car from your Ipod. These adapters can be purchased at any electronic store and is fairly cheap. It looks just like a regular cassette with a wire hang off the end all you do is plug in the wire to your Ipods headphone jack put the cassette adapter in the cassette player then play the cassette and play the Ipod as normal and you should hear the audio from the car speakers.
FM Transmitter this works by plugging the device into the Ipods headphone jack and the audio is then broadcast over to your cars FM radio station. The price range for Ipod FM transmitters vary depending on the brand and features. Some of the fancier ones have readout display, or can even charge your Ipod while its plugged in. Some only offer a few FM channels while the better ones will offer full range of stations to choice from so be sure to buy one that will allow you to play all the FM stations. Scan your FM stereo for a clear station that has no noise or close to no noise as possible. When you find that perfect station number set the Ipod FM transmitter to that number and start playing the Ipod. You will experience some break-up connection and thats pretty normal so its not perfect.
Aux Jack some car stereos come with a auxiliary jack for plugging in your MP3 player, its a little hole in front of the stereo and usually needs 1/8th headphone cable or red and white RCA cables to connect the Ipod to the stereo.