Here's how to use conditional formatting to highlight cells with errors in Excel:

1. Select the cells you want to format:
- Click on the cell you want to start highlighting, then hold down `Ctrl` or `Shift` and use the arrow keys to select the entire range.

2. Go to Conditional Formatting:
- Navigate to the "Home" tab on the Excel ribbon.
- In the "Styles" group, click the dropdown arrow next to "Conditional Formatting."

3. New Rule:
- From the dropdown menu, select "New Rule."

4. Format only cells that contain:
- In the "New Formatting Rule" window, choose "Format only cells that contain" under "Select a Rule Type."

5. Errors:
- Under "Format only cells with," select "Errors" from the dropdown menu. This option identifies cells containing errors like #DIV/0!, #VALUE!, etc.

6. Set your desired formatting (Optional):
- Click the "Format" button to choose how you want to highlight error cells. You can change the fill color, font color, borders, or other formatting options.

7. OK:
- Click "OK" on the "Format Cells" window to apply your chosen formatting.
- Click "OK" again on the "New Formatting Rule" window to confirm the rule.

Now, any cell within your selected range that contains an error will be highlighted with the formatting you chose. This will help you easily identify and address any errors in your data.