I want to start working out since i've had a gym membership for 3 years and never use it.  I want to lose fat and gain definition.  I do not want to "bulk up."

I dont know where to start, what exercises to do (I prefer to use machines as opposed to free weights), how often to exercise, etc.

I'm 44, 5'10", 170lbs and i've started to develop a "belly."

Can anyone give me some pointers to help me start out?