Users can easily install Cirrus Insight for Gmail from the Chrome Web Store.
For further guidance, review How do I install Cirrus Insight?.
Google Admins can automatically install Cirrus Insight for users across the organization. Refer to Google's guidance on how to Automatically install apps and extensions.
After onboarding users, consider setting up Admin-Managed Sync to centrally manage users' Email Sync and Calendar Sync processes and settings.