The resulting pivot table can contain many different entries. By grouping the entries, you can improve the visible result.
Select a cell or range of cells in the pivot table.
Choose Data - Group and Outline - Group.
Depending on the format of the selected cells, either a new group field is added to the pivot table, or you see one of the two Grouping dialogs, either for numeric values, or for date values.
The pivot table must be organized in a way that grouping can be applied.
To remove a grouping, click inside the group, then choose Data - Group and Outline - Ungroup.