After entering a license key that includes Failover features and that designates the machine on which WhatsUp Gold is being installed will serve as the Secondary site, you'll simply continue with the workflow described in Install WhatsUp Gold using either the Standard or Advanced workflow. There are no additional installation dialogs specific to the Secondary Site configuration.
After entering a license key that includes Failover features and that designates the machine on which WhatsUp Gold is being installed will serve as the Primary site, you'll be prompted to complete the following steps at the appropriate points during installation in addition to everything described in Install WhatsUp Gold using either the Standard or Advanced workflow.
Important: When installing WhatsUp Gold in a Failover configuration, you MUST install the Secondary site prior to installing the Primary site.
Important: To successfully complete installation of WhatsUp Gold using Failover features, proceed with Finalize Failover configuration following installation.