Thinking of getting a gym membership

Hey FriendRewind!!! I've been thinking of getting my first ever gym membership, but it's super intimidating to think about as I've literally never been to a gym before. Can I have some tips for gym etiquette when going? I'm not planning to use any weights or stuff since I want to focus on treadmills or ellipticals or stair machines (is that what they're even called?? ), but I still recognize l that I'd be in a public/community space using equipment others might want to as well and want to know how to handle that, as I'm someone that really struggles with human interaction irl 

Also, what clothes do people usually wear at the gym? Would shorts and a random shirt be fine??? People don't care how you dress at the gym as long as it's not inappropriate, right ???