can i connect vinyl with DDJ RB?

Yes, the switch is on the back next to the RCA connectors, then switch the channels to Phono.

Are you 100% sure i can connect TURNTABLE to the DDJ RB? i only see master OUT but not inputs 

Sorry Aleksandar,  Jay must have misread the model.  The DDJ-RB does not have any line or phono inputs.

Is there a setup, so I can use the ddj-rb and 1 or 2 (USB-)turntable so I can combine my mixes with digital music (ddj-rb) and vinyl records?
I assume this is possible with an external mixer, but how?
Could someone inform me if this is possible and what dj mixer do I have to use?

@Maurice > As already noted, the DDJ-RB itself is not capable of accepting any input signal from any device, so you would indeed have to use an external mixer. Virtually any mixer with a phono pre-amp would work, it doesn't have to be DJ-specific, but those typically are more likely to have the phono connections.