Users or groups can be added to any another group. Type group name to find groups you want your group or user to belong, and use "plus" icon to add.
Group or user can belong to other group as a regular user or group, or as administrator. Click on "user" word to change.
Administrator privileges allows to edit group name or to add or remove users from this group.
You can't join a group until you don't have administrative privilege on this group, but you can request a membership You can't leave group or revoke your own administrative privileges until you are the only administrator in this group.
See also: