Go to nyjacks.com for details, or google "jack off club" and search for anecdotes.
Basically, you show up and they give you a ticket after you pay ($25 at ny jacks). You go around the corner and strip to whatever you want to wear. They recommend you put your wallet, phone, etc in your socks (shoes and socks are required to stay on).I suppose that's to avoid any misplacing of crucial items when you check your clothes.
You put your clothes on the provided hanger or, if you're like me, in a backpack and return it to the clothes check guy, who hands you back your half of the corresponding ticket with number. That ticket goes in your sock.
I have read that the minimum is you have to go shirtless, but I've never seen anyone that clothed. You walk around (there are two levels at nyjacks) in whatever state of undress you've chosen ( I'm partial to wearing a Bike jock but sometimes I'm in my briefs). There's a kind of energy that grows. Guys are walking and checking each other out. Lots of guys are jacking on the couch or in a more public space and sooner or later small groups start to form and guys stand in a circle of about 6 maximum and jack each other or themselves. Sometimes guys on the couch will jack in 2's or 3's.
It's a very accepting environment, meaning if you're not interested in a guy, you simply move on, or place your hand on his to move him away, etc. There are all levels of guys and I often feel sorry for the really old guys whom most guys aren't interested in (tho' to be fair, many guys will jack even the oldies), knowing that one day I'll be at that stage. Still, as I say, some dudes will jack the old guys just to be supportive brothers.
You can keep moving around, cock in hand, or you can station yourself and jerk off while watching and if someone comes over to jack with you, that's cool. I like being on my knees in front of a guy on the couch who'll let me tug his balls while I jack his cock.
Cliché, perhaps, but it's really a nice supportive men's atmosphere. Try it.