Grouping by one column
The area above report's list can be used for columns grouping:
To group data by any column just drag this column's header into that area:
Dragging column to this special area will remove column's header from the report's list. Instead, it'll appear in the list itself as list of the values with "+" buttons. I.e. every each one value of the column now became the distinct category. You can expand any category to view reports inside it by clicking on the "+" sign:
Note, that column's header is still visible on the window - so you can still sort data by any visible column.
To revert back to normal view - just drag columns back from special area to report's list.
Grouping by multiple columns
It is also possible to group data by more than one column. To do that just drag several columns in the special area:
You can pick any column and move it around to change grouping order - just like you move column's header in the list.
Note, that instead of grouping you may prefer filtering data.