From the top options in a Site's settings panel, administrators can choose User/Group Access.

Add the Site to a Group
From this panel, you can select what Group the Site should be added to. The advantage of adding a Site to a Group is being able to have that Group's users get access to the Site and to be able to have a collective dashboard and scoring for a Group of Sites.
Select the "Select groups" button below the Group Membership heading to choose Groups that this Site should be added to.
Add Users to the Site
From this panel, you can add User access and permissions for Users already in your DubBot account. Select the "Select Users" button below the User Membership heading to choose Users to add to the Site.