This insight shows you the distribution of users based on their overall activity. In this insight activity is measured by the number of events the user has triggered over all time.
You can create user segments by clicking any of the colored areas in the distribution chart. All your previously created segments are listed in the sidebar on the left. Selecting a segment in the list causes all insights to show information specific to that segment.
When segments are selected this insight shows a separate chart for each segment, letting you compare their proportions to the overall distribution.
Example: Create segments for Least active and Most active users by clicking on the leftmost and rightmost areas in the chart. After the segments have been created, try how selecting them affects other insights such as Characterize and People.