What EXERCISE should I do at the gym? help!?

I am taking summer wellness, and we basically do a lot of sports. Today we did basketball for like an hour, tennis for an hour, and kickball for an hour and a half. It wasn't very strenuous though...I think I should go to the gym still, because I'm trying to lose weight. Should I run, elliptical, lift weight, walk at incline, bike, or what? Thanks.