Groupings can be added to summary, matrix, and joined reports to group together sections of report data. For example, you might want to group accounts by the number of employees that the account has.
To add a summary field, follow the steps as shown:
Drag a field from within the Fields pane.
Drag the field into the grouping section of the Preview pane.
Wait for the loading dialog to complete.
See what the field is showing in the grouping section.
This will produce a report showing the grouped sections, as shown in the following screenshot:
Summary reports can have up to three grouping levels.
Matrix reports can have two rows and two column groupings. You cannot use the same field for both the row and column groupings.
Joined reports can have up to three grouping levels.