While both burned audio CDs and MP3 CDs can both be made in your CD burner, there are differences in how the disc is formatted by your burning software and how many songs the disc will hold.
Generally, when you are preparing to burn a CD, your software will give you the option of making an audio disc or a data disc. If you choose to make an audio disc, you are making a burned audio CD. This will hold fewer songs, but will play in most players.
If you choose to make a data disc, your a probably making an MP3 CD. You will be able to fit more songs onto an MP3 CD, but it may not play on many CD players. To learn how to convert aerobics CDs to MP3 files click here.