The one forum see only registered users and the one admin.
Here's the solution you may set up for your forum:Guests should not be able to even view the forums / Disable viewing of /hide forums unless logged in
But I'm not sure if it wouldn't cross with this:
The users only know reading topics in one forum and post.
It depends on if you'd like to HIDE the forum from the users unless they are logged in, or you'd like to allow to view topics, but not allow to reply in them unless logged-in (in this case, set-up a Registered-only users forums
The users not know create new forum or topics, only the one admin.
Obviously, you will need to make this forum Post-only
The visitors are not know registration, only the one admin know user add.
Possibly you need to disable Registrations. Enable and set $enableNewRegistrations=FALSE;
in setup_options.php for this.
Being logged as admin, you could create accounts manually in this case. Just enter the Registration URL (your_forum_url/index.php?action=registernew
) manually while logged in as admin, and register any new account. You could also create a bookmark for this link for making the process easier, if there would be a lot of accounts on hold.