I go from 5 to 3 times a week depending how much hours I'm working (12h shifts are rough)
Mines rather pricey, 120€ for 3 months but nice atmosphere and not many people so allmost no waiting lines or hassle of getting on a machine.
If you do this for the first time, start easy don't look at other people but yourself. If you want results, you need to go frequently and have some self discipline.
One of the most important things is control your respiration and keeping your back straight and firm during excercises or you'll do more bad than good. This may sound easy but believe me, I've been going for a year now and sometimes I still find myself making mistakes.
Most people train their upper body but training your legs (with machines) are equally important since these are the biggest muscles of your body. If you train them, your body release alot of testosterone and hormones which improve the muscle strength of your entire body.
Normally I do 1 day with machines and the other day cardio (+ punching bag for my french boxing). Or you can do them all in 1 day but e.g, if you trained your arms then let them rest for a day.