I have never used an external display before so I apologize for my ignorance.

Just bought a Dell P2415Q and connected it to my MacBook Pro Retina 2014 and it is working fine. Wondering how to use the P2415Q with the laptop in clamshell mode? I'd like to use my Das Keyboard external keyboard, which requires two USB connections.

Do I connect the keyboard to the P2415Q or the laptop? I have it connected now to the P2415Q and it is not working. Maybe I'm not doing something right.

Any guidance would be appreciated.