Grouping is not a Setup switch. It lives in the report builder, and the format changes the moment the first group lands.
- Open the report in edit mode
From the Reports tab, open the report and click Edit. Starting fresh works too, but pick the report type carefully: it decides which fields you can group by.
- Click Outline
The Outline pane holds GROUP ROWS, GROUP COLUMNS and COLUMNS. The first two lists are where all grouping happens.
- Add the group
Under GROUP ROWS, open the Add group picklist and choose a field. Repeat under GROUP COLUMNS if you want a grid rather than a stack of sections.
- Summarise a field, then save and run
Open a numeric column's menu and pick Summarize, then Sum or Average. Subtotals under each group only appear once something is being summarised.
Up to three levels on a summary or joined report, two once it becomes a matrix.
Adding one flips the report to matrix format. Two is the maximum.
On a date group: day, week, month, quarter, year, plus the fiscal versions.
- A matrix report will not let you use the same field as both a row grouping and a column grouping.
- Removing a grouping breaks any custom summary formula that named it, and you only find out when the report runs.
Keep the related term in your library so you can find this topic again.