#3 Focused and other filters

The Focused filter shows you the emails that you read and respond to the most. The Other filter shows emails that aren't labeled as junk but that you don't read and respond to as often, if at all. The system learns, as time goes on, which emails should be focused on or not focused on.

If you don't have these filters (you are seeing All and Unread instead), you can turn them on via the View ribbon: