If you’re new to the gym, I think it’s a good idea to try out a few different fitness classes to find out what kind of work outs you like the most. Try kickbox, zumba, dance, conditioning, cycling, etc… You can also work on running, or the the eliptical, or the weight machines. Your best results are combing cardio and strength training. Google some beginner’s workout plans for the gym and see if you can find something that works for you.
Best of luck!