The most important concept in vBulletin’s permission system is inheritance. There are several levels at which you may specify usergroup permissions.
The first is at a global level. These permissions can be edited by going to Usergroups > Usergroup Manager > Edit Usergroup.
The permissions you specify here will be used everywhere on the board unless you override them at the forum level. Forum-level permissions can be edited by going to Usergroup > Forum Permissions. Permissions you specify for a forum will also automatically inherit to any child forums, unless overridden there and so on.
Each of these areas will be discussed in detail in the following sections.