User Groups can be used to assign permissions to collections of users. For instance, you can create a User Group called 'sysadmins', and grant that group System Administration rights.

Then, any user you add to that user group will automatically have System Administration rights. You can add or remove users from the group at any time.

System Administration permission is required to change group settings. From the main System Administration menu, follow the "User Groups" link. The top section of the User Groups admin page is used to Add, Delete, or Rename User Groups.

To assign users to groups, use the controls at the bottom of the 'Manage User Groups' page. A user can be assigned to any number of user groups.

Once one or more User Groups have been created, the various Permission setting pages will list the groups, and you can assign rights to the entire group.

And, if you have Calendar Groups defined, you can also set permissions for a Group of Users in a Group of Calendars.