Cash McCall – The Blues

What type of audio file is there in commercially bought music CDs…
and
What is the best free program to convert MP3s into an audio file most commonly played in cd players…

CDs are made using a format called Red Book. You can read more at this:

http://en.wikipedia.org/wiki/Red_Book_(audio_CD_standard)

I use Windows Media Player. There a lots of other programs out there. But Keep in mind that you can burn more songs on to a disc in MP3 format than if you make an audio CD.