Once you've installed and configured your network and allowed user registration, you'll need to make sure that the network is constantly kept up to date, and manage the sites and users on it from time to time.
As a network administrator, you have access to all of the sites in your network and can manage them. There are four screens you can use to do this, and you can access them via the Sites menu link in your network screen screens:
Info
Users
Themes
Settings
Let's take a look at each of them.