MyBB Community Forums

I was wondering do I make it so guests cant view the forum, but when they try to go to the forum page it makes them register or login.

Go to Admin CP --> Manage Groups --> Unregistered / Not Logged In and set the "Can View Board" permission setting to "No." This will not allow any people not logged in to view the forum list. However, there is no message that will be displayed saying "Please register and login to view the board." I think a modification can do that.