Insert the CD-R into the CD-Rom player of the computer. Locate the CD-R icon on the desktop or in the computer's finder function, or user-management tool.
Locate the MP3 file on the hard drive you wish to record to the CD-R. In Windows XP, for example, one option is Windows Explorer (click the "start" in the lower left corner, then "programs" to find Explorer and search for the file).
Click the MP3 file using your mouse and drag it over to the CD-R icon on the desktop (or finder). If working with a PC, open the "My Computer" function from the start menu and locate the CD drive. Drag the MP3 onto the drive icon. Double-click the CD drive to open the drive. Select "Write these files to CD" to record the file to the CD-R.
On a Mac, simply drag the MP3 file over the CD-R icon on the desktop. This automatically opens the CD-R file. Select "Burn" or "Write" to record the file to the CD-R.
Eject the CD-R from the hard drive when recording is complete.