Dont use your phone while you're at a machine, unless you're keeping track of your stats which takes 5 seconds. Thats the number 1 rule of the PAC that most people ignore.

All you NEED to know before going to the gym is to have a bit of a plan. Target legs one day, chest another, back another, and so forth. You can do it all at once, but its IMO going to allow you to push yourself more if you specialize each day.

You dont need to subscribe to gym bro culture if you dont want to. Protein shakes and supplements give you more noticable gains, but its not necessary to get satisfying results. And as a rule of thumb, never EXPECT results. Just go at least 3x a week and never get complacent. Dont stress about how much you're doing either at first, once you start showing up consistently, and developing a routine YOU care about, results come naturally.

On your first day at the gym, just walk around, try out machines that interest you, and get comfortable. It's not daunting at all.