To define a new view, you must visit the menu "Configure special groups" at the end of the policies section of the user account menu. You are presented with a list (originally empty) of configured groups. Use the Add button to add a new configuration.
Pick the group you want to manage and assign a login shell. You may want to pick either /bin/false for unprivileged accounts and /bin/sh for normal accounts.
Once you have define a special group, two new privileges are added and you can grant those privileges to any normal user. He is then allowed to manage this group members. One privilege control general management of the users (changing name, password, redirecting emails, ...). The second privilege let the co-administrator add new accounts.