Whether you have an iPod or any other type of MP3 player, there are a few different ways to listen in your car. Your options are limited by the specific technology you're working with, so it's important to start off by checking into the specific features of the head unit in your car.
Some options are only available if you have an iPod because certain head units are specifically designed to work with those devices. Other options will work with any MP3 player. In order to determine which options are available to you, there are a few things to look for.
If your head unit is specifically designed for use with iPods or other MP3 players, it will typically have a built-in USB cable or jack. Some head units even come with a cable that can plug directly into your iPod.
The next best option is an auxiliary input. Some head units have auxiliary inputs on the back, but those can be inconvenient to reach. If your head unit looks like it has a headphone jack on the front, that's actually an auxiliary line-in jack that you can plug your MP3 player into.
If your head unit doesn't have a USB or line-in connection, you can either use an FM transmitter or a cassette tape adapter. Neither of those methods provide the best audio, but they are viable ways to listen to an MP3 player in your car.