I just bought a brand new wheel to make my Nishiki into a fixed gear bicycle. The guy at the store said it's a flip flop hub which, as far as I can understand, means that one side is fixed and one is a single speed. The wheel came completely naked, no gears or anything. What do I do? How do I make this my dream bike? (Other than put a tube and tire on this bad boy)

You need a cog and a lock ring.