Beginner in need of help

Hey, my name is Greg, and I am looking for some guidance. I have been going to the gym every once in a while, (usually I find i am too lazy) and I am now a sophomore in college, and I have decided to really start a workout routine and stick with it. I have really no background so I dont know where to start.

So, I am 19, about 5'8", 140 lbs. I have a small frame, and the genetics to stay that way, but I seem to gain muscle fast whenever I actually do workout for a few weeks. I seem to have a very fast metabolism, as I have been able to eat entire pints of Ben & Jerry's and never really gain a pound. But now I've started to notice a little belly forming, so I'm assuming my metabolism is finally slowing down some.

Alright so basically I could really use some help and guidance, can someone give me some suggestions on a routine I can begin? I have free access to the gym at my school which is great, it has plenty of equipment. I basically want to reduce my body fat and then begin to build some muscle. Nothing really intense. Thanks in advance

-Greg