Install your recording software on your computer. Most popular programs that are also user-friendly are Cool Edit Pro and Soundforge.
Connect your mixer output into the computer, using RCA-to-USB or RCA-to-3.5mm (or headphone jack). You can purchase this at any electronics accessories store like RadioShack. Plug the headphone jack into the input of the computer so that what you're playing on the DJ equipment records directly into the computer.
Adjust the volume and levels from the music playing into the computer. The music playing on the speakers could be at a different level than the input, and you don't want the recording to peak or sound over-modulated.
Mix the music to your ability. If you have errors, don't stop recording - backtrack the current song that's playing and attempt your mix a second time. With software, you have the ability to edit out any errors or "trainwrecks." This is the case if your mix is longer than the intended amount of time/space on the CD.
Stop recording when you finish your mix. Save the file onto your computer in MP3 or WAV (WAVs use more memory and space) format and give it a name and location that you'll remember.
Listen to the recorded mix and delete any errors, making sure the final draft doesn't sound like an edit. Music production/recording software allows you to zoom in or out of a section of a song as you edit so the end result is practically flawless.
Resave your project and place a blank CD-R in the CD/DVD reader/recording tray of your computer. Burn the mix onto the CD choosing 8x (speed) instead of a faster speed like 12x. This will prevent any skips or misreads as the CD is being burned.
Create labels for your CDs and continue to burn copies of your mixes as needed.