This is a network management tool also known as Multiadmin.

First of all create any amount of site groups. It actually for your convenience only so you can create just 1 group. After that add sites , note that password field is NOT for your admin password (ie password for admin area), you have to type Exchange password from settings of each site.

Custom url is just a custom field where you can enter url to an external rotator or something like that and you'll see that link next to each site.

Sync data - copy all Global Admin info to that new site, useful if you add a new site and want be able to check global stats from each site.