There are MANY options; the big basic question is how techy are you willing to be? I don't know much about good free non-techy ones.. so I'll leave that answer to someone else
The techy-paid answer:
I have tried a few different forum softwares in the past (and made my own from scratch). SimpleMachines (this one) is pretty good, its a bit clunky though. phpBB I think is also a good choice. I would avoid the others unless you want to get into fancy modern forums like Discourse, but those are much harder to setup.
Then you need somewhere to host it! Basically any paid webhost that offers php (all of them) is fine; if you dont wanna pay you can use (https://leprd.space
) although they seem to be out of stock?? Im not sure if anyone knows any other free hosts?
Most hosts offer something called cPanel, its like a web UI that should let you install a forum with RELATIVELY minimal effort; you also need a MySQL database, but your host will also provide that too ^^
Finally, I dunno if you've ever purchased a domain name (like melonland.net) but you'll need one of them too. They cost around $10 a year and you'll need to get one to go along with your forum!
(You can get all of that on namecheap, their smallest shared host "Stellar" would be fine for you: https://www.namecheap.com/hosting/shared/