You "create" a group by assigning a right to it with $wgGroupPermissions. You add users to a group through Special:UserRights. The process is described at http://www.mediawiki.org/wiki/Manual:User_rights
I see. So I would like the "manager" group to have all the rights that the group "users" have and then I would individually assign some more admin rights to the "manager" group. Is there is a easy to specify that the"manager" group has all the rights of the "users" group without having to specify each individual rights as in DefaultSettings.php?