I've been getting into video a lot lately and the amount to learn can sometimes feel overwhelming. Especially right at the beginning. But it's getting better now and I can see light at the end of the tunnel. Incidentally, here's a useful page I ran across today describing codecs. It's just a link to a page in the Apple FCP 7 User Manual which provides an excellent quick read:

Apple FCP 7 User Manual Codecs Page