I have decided to sign up for gym membership. And before I do it I'd like to do everything right with as less as possible mistakes and errors.

I'd like to put on muscle on the right sides. Chest, butt, abs. etc. mainly. I have a flat butt since I sit on a chair almost all day. I'm male. I'm not overweight, though I have high body fat and a bit lower muscle mass but my weight is within normal ranges. Is there anyone here who can help me? I know nothing about lifting, not even the names of the exercises