Gym?

First, ask yourself what your fitness goals are. A gym is a fabulous place to get fit, but it isn't for everyone. Whether the expense, the crowds of people, feeling judgmental, preferring privacy or solitude, all are reasons some people prefer working out at home, or in the local park, or out in nature. On the other hand, gyms offer equipment most people can not afford to own themselves, have classes to teach and encourage you to push yourself, camaraderie of fellow people trying to become fitter themselves, and more.

If you do want to join a gym, be aware that most gyms offer free tutorials in not only what amenities they offer, but usually a trainer will show you how to use equipment you are unfamiliar with, even help setup a routine for you to follow. This may be free, may be a one-time expense, but often is well worth the investment to get started.

Are you asking where to start with gym specifically, or where to start with improving fitness, how to use exercise to support health or weight loss, or something that isn't one of those? Those are all really different goals, with different best "where to start".

I'm pretty fit for an old gal, rarely visit the actual gym, and lately most often when I do it's to sit in the sauna, because aaaahhhh, nice.

There's good advice above about what to do if you meant gym specifically. But if your actual main goal is improving fitness, improving health, getting stronger, supporting a weight loss effort, simply getting more active . . . we could give more nuanced advice if we knew more about your specific goals.

Best wishes!