Get some DJ software and load it onto your laptop computer. The most popular program is Serato Scratch but Traktor is a slightly cheaper alternative that is arguably just as good.
Follow the set-up prompts to get the software up and running and link it to your the music library on your computer. Once you have set up your program you will have full access to all your music files on your DJ software.
Boot up your DJ software. Find and activate preferences under the software menu. Set the preferences for the built-in input. Plug your computer into the sound system via the headphone jack on your computer using the quarter inch to RCA cable.
Find and select iTunes under the track collection menu on your DJ software. Find the tracks you would like to play and drag and drop them in the two channels shown on your DJ software screen interface.
Return to preferences under the command menu and select output routing. Set it for internal to activate the mixer on your DJ software. You are now ready to DJ anywhere and any time using nothing more than your laptop computer.