My brother is playing Minecraft for the xbox 360 and he has heard about Enderman but he can't find any. I keep trying to find a website that has the answer to my question, but we don't know if you have to do something before you can get one or if you have to go look for it. (Sorry, we just got the game so we don't know very much about it.)
Unfortunately, Endermen do not currently exist in the Xbox version of Minecraft, though they are (presumably) planned (along with everything else the PC version has the Xbox version hasn't).
The PC version of Minecraft is (at the time of this writing) release version 1.2.5, the Xbox version is roughly beta 1.6, and Endermen were added in beta 1.8.