2. If you have set up event tracking correctly, you can now navigate to your Events Overview in Google Analytics (Behavior > Events) and you shall see all your events. You can group events in categories if you like. You now have to define Advanced Segments to group the users who take certain actions (e.g. "invite a friend") into a separate user segment. Go back to the Cohort Analysis page, and click on Add Segment and then New Segment (red button)