Locate the "Master Out" or "Booth Out" jacks at the back of your mixer. The labels differ depending on the type of mixer you have, but there will be one red and one white RCA jack, used to send the mixed-down sound out to speakers or other device.
Plug the red and white cables into the corresponding outputs on the mixer. The other end of the converter should be a mini stereo connection, which have two black horizontal rings on the metallic tip.
Plug the mini stereo connection into the "Line In" jack on your soundcard. Most soundcards have both a "Line In" and a "Line Out" jack, and the "In" one is usually colored blue. If you do not have a soundcard, you can plug the cable into the "Mic" input (usually pink), but you this will only record in mono. The best sound quality is achieved by going through the soundcard.
Check that the "Line In" input is selected for recording on your computer. On Windows, go to "Control Panel" and then "Sound" or "Hardware and Sound" (depending on your chosen layout. If you have "Hardware and Sound," go to "Manage Audio Devices" next). Click the "Recording" tab at the top of the window. Click "Line In" and then "Set as Default." You can also click "Properties" to check the levels and make certain that the "Line In" channel isn't muted.
Download some recording software. There are many options for recording software online, such as Audacity, GoldWave and MixPad. This will be used to make your recording. Wiring up your mixer to your PC routes the audio to your PC, and your software will give you the opportunity of tweaking your recording if necessary.
Open the software and click on the "Record" button. This should be the familiar record symbol, but you should refer to your specific product's instructions if the button isn't clearly marked. When you press "Record," you should start to play your DJ Set using your turntables. From your digitized recording you can burn copies onto CDs or post your set online.