How to sum data from different Excel sheets?

It is referred to as to consolidate data from multiple sheets into a master sheet.

1. Drag your mouse to select the cells corresponding to those in multiple sheets. Note: It would not work if you click the top-left corner box.
2. Date | Consolidate.
3. Click the icon under 'Reference'.
4. Go to the first data sheet, and drag-select all the cells. Click the icon again. Click 'Add'.
5. Go to the second data sheet, and repeat Step 4. Repeat until all the data sheets are done.
6. Click OK.

Done.

In addition to 'Addition', you can also do average, counting, max, min, product, etc.