Hey Bill - Welcome to the 21st century! You sure the electrical system of your Jag can handle a mp3 player? Where did you get a 6 volt head unit? ha, ha, ha
Here are some useful facts:
Regular music CD's are "ripped" into MP3 (and many other) formats for easier digital handling. You'll need ripping software to convert your music cd collection into a digital library of MP3 files. A free one is iTunes from Apple (default file format for iTunes is not MP3). This process is basically you sitting by your computer and feeding it your CD collection. A fast computer with a fast drive is appreciated during this process. Most software provides a "x" rating (no, not that) that indicates speed. A "10x" rip means that the computer is reading and converting the music at 10 times normal play speed. For this, faster is better.
Once this step is complete and you have your digital library available, you can "burn" CDs. (there are other ways to create a digital library including buying them online...Be aware that all the people that "own" the music probably don't agree on what is fair/legal/ethical as far as fair use goes....).
Burning involves copying the MP3 (or other format) files from your digital library to a CD. This process is pretty straightforward and is similar to creating data CDs.
All digital formats are not created equally and even all MP3 formats are not interchangeable (the MP3 format from Apple, used by iTunes, is non-standard for the industry and most non-apple mp3 players don't recognize it). Plus most formats allow the user to tweak them. During ripping, you can adjust some of the "encoding" variables, including bit rate and how the song names are stored. Bit rate allows you to encode the song at a higher quality. The "bit rate" is the rate at which the music is sampled and stored. The higher the rate, the more data is needed for a given song (the bigger the MP3 file). For playing in you car, the default rate of your ripper is fine.
The easiest way to accomplish this is to buy a $30 program that manages all the aspects of CD/DVD creation. Roxio and Nero are two examples.
Rock on!