At first, you must understand five elemental things which are User, Group, Rank, Avatar, Permission. This section explains the basic of them to you. For more informations, you should read each sections.
This is meaning a user account. A user account has login informations on Xoops Authentication and fixed profile fields. Uname, E-mail address and Password are must to work this site. User accounts are added by administration and User Registration.
This is meaning a group of user accounts. A user account can belong to plural groups. A group has Permission for modules. In this module, the thing having permissions is not users but groups. Permissions of users are decided by groups which users belong to.
You may create groups for both of permission management and user list. But, you must know three fixed-groups. These special groups have been created in the installation, and it's unpossible to delete.
Users belonging has the permission to do anything. In other words, users which can belong to this group are the webmaster only. You pay attention to that this groups are allowed to do anything. In case where you hope to leave your friends a part of site management, you don't put your friends to this group.
Let me say that again. This group has the permission to do anything.
Common users belong to this module. User Registration of this module uses this group as an initial group which a new user belongs to. In most of cases, you should not give admin permissions to this group.
Access which doesn't login is handled as this group. This group is really special group and a kind of virtual groups. This group should not have members.
Rank is one of user's profiles. Rank consists of the symbol image and the title. A rank of a user is decided by number of his posts. This feature is a kind of jokes which make your site exciting. Therefore, you don't need to worry that ranks give some effects to Xoops Authentication.
Avatar is one of user's profiles, too. This is a personal graphical label. There is two kinds of avatars. One of them is System Avatar, which administrators prepare. Another one is Custom Avatar, which users upload their favorite image file.
Permission is action permissions of groups. This module can edit the basic of permissions. If you hope to edit module-specific permissions, use the permission editor of each modules.
Permissions of a user are decided by union of all group permissions which a user belongs to.