By clicking Groups And Roles, you will see the Organization form which allows you to manage users, groups and memberships.
As an administrator, you can easily find, edit information of users, and even remove them from the system via the User Management tab. By default, all registered users will be shown in this tab.
Via the User Management tab, you also can define each user belonging to user groups and his memberships (roles) in these groups. You cannot add users to a group but can remove them from the group.