A Pivot Table is a special tool in Excel for summarizing data without formulas. The Pivot Table interface behaves like a report generator, allowing you to interactively add and remove fields as you like. The screen below shows the how fields have been configured to build the pivot table shown above.
When data changes, you can simply refresh the pivot table to see a new summary. Pivot tables automatically group data using field values.
For more details and examples, see Excel Pivot Tables.