Callisto Installation (1901+)
There's some minor pre-reqs to install detailed here

The Callisto installation routine will complete all activities to install and complete the initial configuration of Callisto.
The welcome screen allow you to select your installation folder and paste in your Callisto trial/retail key. You can review the license details and accept them.

Callisto requires its own database to hold configuration and user details. This can be stored on a local or remote SQL instance. SQL Express is supported. The database installer screen allows you to browse or type in the details of the SQL server and instance if required. You can test connectivity to the selected SQL instance before continuing.

Enter the IIS port Callisto should run on. This can be changed later in IIS Admin, the default port of 80 should be changed to an unused port if there is an existing website or a Configuration Manager MP/DP on the server you are installing on.

On this screen you can provide the details for the server and database names of the System Center databases you want to connect to. If you are only using the Configuration Manager functionality of Callisto, simply leave the others blank.
Completing this screen automatically populated the database connection strings on the Callisto Administration node, these can all be changed later as required.

Once Callisto is successfully installed you can click the first link in this page to launch the site, a start menu item is also created.
Be sure to complete the database permission requirements for the System Center databases as detailed in this KB article