Rane SL3 with DJM 900 and 2 CDJ 2000s

i have to set up some gear for a party this weekend but the DJ uses serato they requested a SL3, I can't seem to find a answer on the internet for some reason, but how exactly does the SL3 plug in to everything ? I'm just a usb and go guy so i have never done this. 

what plugs in to the input and what where does the output go into ?

does the usb from the sl3 go into the mixer or the cdj

I'm just wondering basic hookup because i can't seem to find a straight answer anywhere, just trouble shooting stuff.