Have you tried reading the manual?
Access masks allow you to set permissions for individual users.
http://www.vbulletin.com/docs/html/users_access_masks
Forum Permissions lets you set access to certain forums for certain usergroups.
http://www.vbulletin.com/docs/html/u...anaging_forum_
Placing someone in the super moderators usergroup enables you to give them access to the modcp.
Administrator Permissions gives you the ability to control access within you AdminCP, you need to place the user in the Administrators usergroup then using the Administrators permission page set access to certain areas. (E.g. Styles and Templates/ Plugins/ Users e.t.c.)
http://www.vbulletin.com/docs/html/u...up_admin_perms
Its not that hard once you get your head round it.