cda to mp3 files, won't go on iTunes!

I have a macbook air without a cd drive, so I couldnt play my CD on it. Instead i uploaded the CD files onto a PC, then copied them onto a memory stick. Then I put the memory stick into my macbook and copied the files from there and saved them on it. The only problem is, now the files from the CD are in my computer but I'm pretty sure they are cda files not mp3 files so they wont play, or go on iTunes. How do I get my music on iTunes (as in I guess I have to put them in mp3, but I don't know how).

If anyone could, it would be greatly appreciated!

Thanks!