Have you had an induction? Many gyms will include making you a plan up as part of your membership, some lazy ones probably won’t I can give you a decent start though..
Start with a 10 min warmup, treadmill, bike, something like that, just to get your heart rate going. Stretch before
Move on to weights, this will vary massively on what your gym has. Don’t worry about doing certain days on different parts of you body and that, as a beginner it doesn’t really matter. Pick out a routine of machines that target body parts you want to work, and then aim for 3 sets of 12 reps on each. Remember that it’s not about weight so much, you want to make sure you do all 3 sets in clean reps with good form, that’s miles more important than how much weight is on. If you’re struggling to do that, weight goes down and then build slowly from there
Last thing is to finish off with 30-45 mins of cardio. You can do it on one machine or split it, the important thing is how hard you’re working. Google heart rate training zones, you stick in your age and weight etc and it will tell you where you want your heart rate to be to work effectively, most modern equipment has sensors on that you can use to monitor it, and then the aim is to stick in that zone for the entire time which you’ll figure out by changing your speed and resistance
It’s pretty daunting starting the gym and knowing nothing about it, but if you stick at it you’ll pick loads up just watching and talking to people, new exercises, how to use other machines etc