The administer Users section is where you can view Forum specific information for the Users of your Forum.
You can manage user information and spam registrations.
Simple:Press Forum does not maintain its own User database. It shares the same User database as your WordPress blog.
A User of your WordPress blog is a User of the Forum and vice versa. If you want to add, edit or delete users of your Forum, you need to do that from the WordPress User Management admin page.