help again lol

[RookieCraft]

It's me, requesting help again.

So, this time i need help with adding a portal page like this: http://prntscr.com/erd21o when you go to mysite.com (mysite.com replaced with my domain) and you go to forums.mysite.com to access the forums (xenforo)

 

[DarkKnight]

- Make a subdomain and put all the forum related files there
- Upload your portal to the root web directory (i.e public_html)
- Update the portal links to direct to your subdomain

 

[RookieCraft]

- Make a subdomain and put all the forum related files there
- Upload your portal to the root web directory (i.e public_html)
- Update the portal links to direct to your subdomain

How do I add the subdomain? just add a file in the ftp called forums.mysite.com? or what? and what files do i move in there? im confused so much lol