Managers have administrative privileges over every aspect of the circle experience. They can access all sub circles (public and private) and circle settings and they can delete member posts. When you have layers of nested circles, managers can access every circle within the hierarchy.
To add a manager to your circle, click on the gear icon in the top right hand corner and select Settings. Now select Circle managers and click on the green Add managers button.
To add a manager, they must have an existing account on Sutra. You then add them by typing @ followed by their username.