Forum Public Permissions
The forum categories, threads and comments are public, but to send a comment or create threads, users must be logged in, and should have a Role that contains the right permissions to do it.
Then all public forum permissions list:
Moreover there are lots of forum permissions for manage access to forum administration comfortably.
How it works?
Forum has Categories to sort out your posts into them and get have very organized forum.
The usage is very simple, simply access to administration panel, and then you can start creating categories and threads.