Administrators with unrestricted access to the Discussion Forum Categories feature in System Roles (Manage Features > Community Manager Features) can create forum categories.
After creating a new forum category, you must configure its target audience and, if required, its access permissions for other administrators.
For other administrators to assign their forums to a forum category you have created, give them read-only access to the category.
To create a discussion forum category
Additional Information
Edit a Discussion Forum Category
Delete a Discussion Forum Category