First you'll need water skis. There are four types: combination pairs, slalom, tick, and jump skis. New skiers should start with combination pairs, since they are wider and easiest to learn on. Make sure your skis have been checked and that they fit properly. You will also need a flexible towrope that has a floating handle.
All water skiers wear life vests (a.k.a. personal floatation devices or PFDs). You should wear a special water skiing life vest that is approved by the Coast Guard. You and your parents should check this out to get the official word on which life vest is right for you.
Finally, since you're outside, you need to guard against the sun. Want more info on gear for staying sun proof?