The Super Admin is the user who creates all the individual blogs and sites, administers theme availability for those individual sites, and is generally responsible for the health of the entire blog or site network. The Super Admin has many more right than typical users, even the administrator users for individual blogs or sites.
When you first login as the Super Admin, you'll see the WordPress Dashboard window just as you normally would. This dashboard is for the "root" site. Say your root site is http://multisite.longren.org, with individual blogs sitting at http://multisite.longren.org/sydney/. In the default Dashboard window the Super Admin will allow users to edit the contents of http://multisite.longren.org/. They can add pages, posts, and all the normal things you'd be able to do on a regular, single-site WordPress installation.
This default Dashboard window can be seen in the following screenshot:
Initial Super Admin login dashboard
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