Click the "Burn" button at the top of Windows Media Player. The right side of the screen should be labeled as the "Burn List."
Click the arrow directly under the "Burn" button. A menu will appear.
Select "Audio CD" from the menu. This is the option needed to convert MP3 files into audio CD format. The "Data CD and DVD" option will directly place the music files onto the CD or DVD in their original format.
Drag the MP3 files from the song list in the middle of the screen to the burn list. This only queues the songs to be burned, they will not be converted at this point.
Insert the blank CD-R disc into the CD burner on your computer.
Click the "Start Burn" button at the bottom of the burn list. Each song will be converted from MP3 format to audio CD format and burned to the CD.