MyBB Community Forums

This has nothing to do with mybb but people here are very smart as I’m still learning a little but some people have www.forums.website.com then some have www.website.com/forums/ how do you do it the www.forums.website.com?

in brief
required subdomain is created at the server through web host control panel and
subfolder (domain.com/forums) is redirected to the subdomain (forums.domain.com)

Edit: have a look at a few search results for more details