Best way to get started in the gym is to get a couple of sessions with a personal trainer. Set yourself attainable goals and don't worry about comparing yourself to the few (very few) of us who go 5 times a week. A lot of people you'll see in the gym use it regularly...that's only because they're the only ones who use it...everyone else pays up an never goes.
Train 3 times a week to start off with and leave a day between each session. Overtraining is not only the easiest way to get injured, but it's an even easier way to lose interest.
A personal trainer will design a programme that suits you, your current fitness levels and your goals. Stick to it 3 times a week for 8 weeks and I can't over-estimate how good you'll be feeling. Then you'll be hooked...just like the rest of us.