1. To be victorious in some competitive event or activity. I don't normally win at debates like these, but I felt really confident and well prepared. My parents always let us win at board games when we were really little.

2. To earn some kind of prize or reward at a competitive event or activity. In this usage, a noun or pronoun is used between "win" and "at." I won a stuffed bear at the target-shooting game at the state fair. He won a nice little sum of money at the national spelling bee.