White to play and win:

why cant i play this?

Its a diagram, not a puzzle, you're meant to play it through offline or whatever you want and then post the moves, just so people actually have to play it through and not just say they did. I guess.

yeah, i guess, but it's annoying not to be able to look at the answer if you can't figure it out.

1. Nc6 followed by Ne5 if Black plays ...Nh3, and Nb4 if ...Nf3.

The black king is in the dark square. Was it intentional or just mistake?

Intentional

Correct!

Incorrect, 2. Nb5 is not even possible, 3. ... Ne5xd3

Ne5 Qx e5