Arguably the most important part of a forum is its user base. XenForo contains a wide range of user management tools in the Users section of the admin control panel.
This section covers the more complex features that relate to users in XenForo.
Custom user fields
When XenForo needs to test something (user/page/post...) against some user-selected conditions (criteria), it uses the Criteria system.
Some places, where the Criteria system is used:
Addons can also use this system.