@ Bes- You need to make a bracketmaker account (Link)
From there, you follow Ryan-'s links, and click the small "Predict It!" link in the upper left hand corner, and follow the instructions on the page about choosing your votes. (it's pretty easy, you just click whichever person you think will win, then press "enter" when you've completed each round.)
@ everyone else- Good luck in the cup, it should be a good one.