if you want to play mp3 files on a normal cd player (like a car one) that doesn't have support for mp3, you need to burn it as a native audio CD. Use iTunes or Windows Media player or your favorite burning software to do this.
If this is just transfer to another PC, you can just copy the mp3s over, but you'll need the codecs for it, as well as have that target pc authorized to play it if its DRM protected. Codecs can be downloaded from the net. Just search/google for Audio codecs or K-lite Media pack or something.