Things that satisfy you or make you happy are rewarding. Even if you love to learn, the most rewarding part of going to school for many of us is making good friends.
The word reward is obvious when you look at the adjective rewarding, and rewarding things do give you a kind of reward. Rather than cash for finding a neighbor's lost cat, though, the reward you get from something rewarding is pleasure or satisfaction. Watching a great movie is rewarding, and so is doing something kind for another person. You might even get lucky and have a rewarding career, or even a rewarding life.