Groups allow you to quickly segment rows, or pivot in your data sets. Grouping organizes rows by a specified categorical column, and collapses rows that meet the specified criteria. Groups provide similar functionality to traditional pivot tables, but are easier to navigate. To the right of each group you'll see a count of the number of rows within the group.

You can create nested groups, and rearrange the group hierarchy via the bar at the top of the sheet, or in the Group panel.

Check out this detailed video that shows how to use Groups in your analysis: