To stay on the safe side, you should do an induction class.
Or if you're less wise, stick to safe exercises like bench presses or leg presses which, if you're warmed up properly, shouldn't be too dangerous. If a trainer is around and you're curious about one exercise in particular, just ask quickly or even ask someone who's working out too.
Then again, in a gym, everything is dangerous, even after an induction class, unless you're constantly supervised by a professional trainer, not any trainer unfortunately. The majority of people in gyms aren't doing the exercises properly but most will have no consequences whatsoever.
For several years I did cable lateral pulldowns behind my neck because my trainer told me to. I recently found out most experts highly discourage doing that. No wonder, I've got pretty bad back problems now.