You need to go to OPTIONS > USERS > CHANGE PERMISSIONS.
By default, Nabble allows anyone to see (View) your forum post new messages (Create_topic) and reply (Reply) to existing messages. They don't even need to register! Hence "Anyone" has these permissions by default.
As it is convention for forums to require registration before posting, Nabble also provides a higher class of user called "Registered". By default the only additional permission that class has is to see the list of registered users. However, the expectation is that you would remove the permission of "Anyone" (i.e. the general public) to post and reply and add those permissions to the "Registered" group. Some forums would not even allow the public to view the contents of the forum, hence the "View" permission might be removed from "Anyone" as well. In such cases anyone visiting the forum's URL would be met with a Login screen.
Registering is the only automated change of status. It occurs when a user clicks on the link in the email they receive after following the Register link and supplying an email address. (You can get an email notifying you of new registrations via OPTIONS > APPLICATION > EXTRAS & ADD-ONS > EMAIL & NOTIFICATIONS.) All other changes in Group membership require an administrator to make the change. Apart from the four default Groups "Anyone", "Registered" "Administrator" and "Member" you may add any others that you wish and set permissions as required.
Many forums will offer additional benefits to those who pay a fee or contribute in some other way to the community. Typically, such a status would allow them to see and post in additional areas (sub-forums in Nabble jargon) which may not even be visible to the public or registered users. Nabble allows for this with its predefined group called "Members". As with the Registered group, by default this only has one additional permission, to see members.
If you wish to implement such a two tier membership, first you need to create a sub-forum and set member permissions for that sub-forum to remove the ability of those in the "Anyone" or "Registered" group to view (possibly!), post or reply from it, while adding those permissions to the "Members" group. In this Support forum, it is done in reverse. "Anyone" can view both the Premium and Free forums. "Registered" can additionally, post and reply in the Free sub-forum, but only "Members" can post and reply in the Premium forum.
Note how, at the top-level forum, you can either keep the "Default" permission for any setting or change it to a "Custom" value, but for a sub-forum, the default is to "Inherit" its settings from its parent forum, although, as with the top level forum, you can set a "Custom" value for any setting.
In summary, you might want to think of it as designed to enable you to create a system where:
Anyone = The General Public
Registered = Those who have supplied a valid email address
Members = Registered users with Added Benefits
However, Nabble is entirely flexible. On some of my forums I have such groups as "Sellers" (for those I permit to post in a single "For Sale" sub-forum, but I don't wish to spam everywhere), "Moderators" (for colleagues who can move messages to a sub-forum hidden to other users while we decide how to handle suspect messages) and "Invites" (For filling with addresses of those members of the mail list software used previously - effectively pre-approving them). With these groups I create a special set of permissions that distinguish them from both registered and any awarded additional member privileges.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.
Locked
)