Reply to mixing with only laptop(usb) and a mixer

Hi!
I am a total rookie in the world of digital dj'ing. Anyways, i decided to just go ahead and buy a Behringer vmx200 usb pro mixer, believeing that i then could easily mix music straight from my laptop via usb without anything else.
Funny enough i cant make it work. i am using traktor software, but i can only get the 2 decks from traktor to play in the one channel in the mixer.

Does anyone know if it is even possible for me to mix with both 2 channels in my mixer, with the usb from my laptop as the only input??
I wonder if i just need the right setup in traktor (fx a tks file), which is what i hope

cheers