Users who access Outlook online via browser (like Chrome) can easily install Cirrus Insight for Office 365 using the steps in this guide:
How do I install Cirrus Insight for Office 365?
After installation, Cirrus Insight will appear in Outlook online when accessed by browser, as well as the desktop clients Outlook for Windows or Outlook for Mac.
Admins can deploy Cirrus Insight across the entire Office 365 domain using the steps in this guide:
For Admins: How do I install Cirrus Insight for Office 365 for my users?