Site is a physical location. Its a place where you can place a container. A Site can have more than 1 container. If you use Sites (some only uses containers), remember you first have to add a site, then you have to go to "manage Containers" and place 1 or more containers on this site. Important if you under "manage containers" edit a container and place it on a new site, the container will automatically inherit the address from the site even if the container previously had a different address.