Go on their website, which I believe is collegeboard.com and bring with you all the required documents, and more!
My mum always makes us go with a folder filled with documents whenever we're going somewhere important. Better safe than sorry right.
Know of a person who wasn't allowed to take the test because he didn't have his passport, although he had his drivers license. Seems trivial, but he had no chocie and had to pay a fee to change his exam date.