You can format cells based on whether their values are greater than, less than, or equal to a certain number using Conditional Formatting in Excel. Here's how:

1. Select the cells you want to format: Click and drag to highlight the cells you want to apply the formatting rule to.

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

3. Choose "Highlight Cells Rules" or "New Rule":
- Highlight Cells Rules: This provides pre-defined options based on values. Select the appropriate option like "Greater Than..." or "Less Than..." depending on your need.
- New Rule: This offers more flexibility for creating custom formatting rules.

4. Format cells based on value (New Rule method):
- If you chose "New Rule," select "Format only cells that contain" from the first dropdown menu.
- In the second dropdown, choose the comparison operator you want:
- Greater Than (>)
- Less Than (<)
- Equal To (=)
- Greater Than or Equal To (>=)
- Less Than or Equal To (<=)
- In the next box, enter the specific number you want to compare the cell values to.

5. Set the formatting (both methods):
- Click the "Format..." button. This opens the "Format Cells" window where you can choose the desired formatting for cells that meet the condition. You can change font color, fill color, borders, etc.
- Once you've chosen your formatting options, click "OK" to close the "Format Cells" window.

6. Finalize the rule (both methods):
- Click "OK" in the "Conditional Formatting Rules Manager" window (for "New Rule") or "Highlight Cells Rules" window to apply the formatting rule to your selected cells.

Now, cells that meet your comparison criteria (greater than, less than, or equal to) will be formatted with the style you defined, making it visually easier to identify those values within your spreadsheet.