When working with large numbers, it is often useful to format them in scientific notation. This can be done using the "Format Cells" dialog box in Excel. Here's how:

1. Select the cells that you want to format.
2. Click the "Home" tab on the ribbon.
3. Click the "Number" drop-down arrow in the "Number" group.
4. Click "More Number Formats" at the bottom of the list.
5. In the "Category" list, click "Scientific."
6. In the "Decimal places" box, type the number of decimal places that you want to display.
7. Click "OK."