If they are using a controller it will be like thatpartydj said. However, If they are using timecode they will unplug the cdjs and route them through a sound card of their own. If they change the setup they should be changing it back at the end of their set, so you shouldn't have to be worrying about it too much. However when I'm on the computer I'll grab a diagram of how timecode is wired up so you can at least be familiar with what's going on