Ensure the mixer and CD players are turned off. The mixer should have labeled "Channel 1" and "Channel 2" inputs on the rear. Connect the left CD player to Channel 1 and the right one to Channel 2. Connect both players and the mixer to the power outlet. Boot up the laptop and allow it to fully start the operating system.
Locate and identify the connections on the rear of the mixer. A basic model will likely only have a phono master output and 1/4-inch microphone input. More advanced mixers may have dedicated effects send and return sockets. It may also have more than one channel. Three channel mixers are quite common in clubs. Identify the connections present and ensure you have the correct cables.
Connect the laptop's headphone output to the channel 3 input to use it as an additional playback device. You can cue up songs in a standard media player and use the mixer's faders and equalization controls, just as if it was an additional CD player.
Record your sets live, by connecting the master output from the mixer to the microphone input on the laptop. You can then run a second cable from the headphone output to the PA system.
Use the laptop as an effects unit for vocals, connect the send socket to the microphone in put on the laptop and the return socket to the headphone output. Launch the effects processing software on the laptop and connect a microphone to the dedicated input on the mixer. Everything said through the microphone will be processed on the laptop before being routed back to the mixer.