You can add forums to your guild site on the Admin menu:
- Click Features.
- Click Forums from the column on the left.
- Click Forums again from the menu that appears (this is the actual link that will bring you to the Forums tab).
- Click Create Forum under the category where you would like to add the new forum.
From here, you need to enter a few details:
- The forum name
- A short description of the forum (like "Post raid strategies here!" or "For anything not relating to badgers.")
You can also establish whether or not it's a subforum to a current forum, change the category, etc.
Once you've done this, click the Create new forum button and you're done!