Where a user registration must be approved by a conference administrator or moderator before the user can enter a conference. Where all users are required to enter valid usernames and passwords in order to enter a conference. You manage permissions at the conference and forum level. Permissions are assigned to user groups. And since all users are members of at least one group, you manage access to conference features by managing group permissions.
Users inherit the permissions assigned to their group.
Group permissions include the ability to access a specific conference, create message threads, or post replies to existing messages. Forums, which are discussion areas within a conference, can be assigned to multiple conferences. By the same token, you can limit which forums are available to particular conferences. When users enter a conference, they only see the forums an administrator has explicitly defined for that conference.