Managers are only able to view sites in which they are assigned. Sites may be assigned by administrator users only. Administrator users are able to access all sites.
There are two ways to assign sites to managers.
1. Search for the site and open up the site details. Click on the "Admin" tab. Search for the manager that needs access to the site and click on the "Save" button. The manager should now have access to view the site.
2. Click on the "Admin" tab and choose "My Users", and search for the user that needs access to the site. Open the user details and click on the "Assign Sites" button. Chose the sites that the manager needs access to. To choose all sites, click on the top left checkbox and all sites are highlighted.