Set the turntables on either side of the DJ mixer. Plug the left turntable's RCA output into the phono input of the first channel on the DJ mixer. Plug the right turntable's RCA output into the phono input of the second or third channel, depending on the mixer's capabilities and number of channels.
Set the laptop to either side of the turntables or behind the mixer. Many DJs choose to use a laptop stand for easy access to the computer. Use an RCA-to-1/8th-inch adapter to connect the laptop to the remaining open channel if there are more than two or to a line input on either of the channels.
Plug in power cords to an appropriate power supply. Double-check the audio connections to make sure everything is correctly in place. Plug in the headphones.
Connect the DJ mixer to a stereo or speaker system using the mixer's "master" output. Turn the speaker system on and reduce the channel levels of the DJ mixer. Turn the mixer and the turntables on.
Begin playing a record on one of the tables and slowly push the corresponding channel fader up to increase volume. Adjust the equalizer knobs as needed. Repeat for the second turntable once satisfied with the first.
Turn the laptop on and begin playing an Mp3 or desired audio file. Switch the channel to "line" from "phono" if the laptop is connected to the same channel as one of the turntables. Use the channel fader along with the equalizer knobs to bring the audio from the laptop to an appropriate level.
Use the mixer's cross fader and channel faders along with the headphones to cue new tracks and blend songs together. Use the laptop to play additional music or to play sound effects to add interest to the mix.