As Rick said, easiest way if you have never done it before will be to use Windows Media Player (WMP).

Put the CD in your computer and open WMP and click RIP. You should see a list of songs that are on the CD, all with ticks next to them. Go to the TOOLS menu (along top of WMP) and select OPTIONS. Then click the tab with RIP on it and make sure it is set to MP3.

Then, back in the RIP part of WMP, press the RIP CD (or similar) button. Each track will then be copied and converted to MP3 format, one at a time, to your computer.

Do this for each album.

Then, when all is done. put a blank CD in the computer. Go to the folder where the music was written to (by default, this should be MY MUSIC, in MY DOCUMENTS) and highlight all the tracks, and right click on one and select SEND TO, and you should see a small picture of your computer CD drive and some text (be the name of the drive usually) Click this and it should start copying all the tracks to a new window. Might take some time.

Anyway, when it's done, all you need to do is click the WRITE FILES TO CD in that new window and it should copy them all onto your disc and you should have a nice MP3 disc to play in the car