Test your DJ mixing setup to ensure it has everything you need to get started. It would be a separate tutorial in its own right to explain how to arrange the items you'd need to perform your mix, but if you've come to the point of wanting to record one, let's assume you already have at least a basic DJ setup near your computer. Play a few records or CDs to test out the sound.
Locate the stereo outputs on your mixer and connect the stereo RCA ends of the Y-cable to them. Most mixers have an array of inputs and outputs on the back of the console. The outputs you want are most likely labeled "Master Out" or "Booth Monitor," either of which is designed to send the mixed stereo signal to the destination of your choice. Connect the two stereo RCA cable ends, making sure to match the left cable end to the left output and the right cable end to the right output. The ends of the cables and the outputs are often color-coded to make matching connections easy.
Locate the "Line In" input on your computer and connect the single headphone end of the Y-cable to it. On desktop computers, you usually can find this input on the back of the computer tower, and often it is colored blue. Most newer laptops also have a "Line In" input, but if you're unsure which it is, check with the documentation that came with your computer.
Configure your computer to record using the "Line In" input. On a Windows PC, this will be set in your "Volume Control" panel, while on Mac OS X you will find it under the "System Preference," then "Sound" Select "Analog Mix" or "Line In" as your sound input source. The exact names of audio control panels and options will vary depending on which version of an operating system you are running, so check with your system's vendor if you are having trouble with this step. It is worth getting to know this control panel well--it often can be helpful when troubleshooting sound issues that may arise later.
Start your recording software and open a new file or track to test recording. Most audio recording applications have a familiar interface with a large red button that starts recording. Start playing a piece of music on your DJ setup and press this button. Depending on the software you have, you may see a visual indicator of audio input levels as well as the waveform itself being drawn on screen.
Stop recording after a few seconds and play back what you just recorded. If you recorded the sound from your mixer perfectly, you're all set. If not, review the previous steps and begin troubleshooting what may have gone wrong.