After downloading, run the installer by clicking CirrusInsightForOutlook.msi (which should appear at the bottom of your browser).
If you don't see the download in your browser, navigate to the folder you chose to download the file to and double-click the CirrusInsightForOutlook.msi file.
Select the Run button to launch the installation wizard.
Follow the steps in the wizard and install in the default location.
Accept the terms of the agreement and then click Next.
After installation is complete, open Outlook (or close and re-open if it was already open). Then sign in from the Cirrus Insight sidebar in your inbox.