Here's how to create conditional formatting rules to identify cells above or below a standard deviation in Excel:

1. Select the data range: Choose the cells containing the data you want to analyze.

2. Go to Conditional Formatting: Navigate to the "Home" tab and click on "Conditional Formatting" in the "Styles" group.

3. New Rule: Select "New Rule" from the dropdown menu.

4. "Format values by rule" option: In the "New Formatting Rule" window, choose the option "Format values by rule."

5. Less Than or Greater Than: Depending on which values you want to highlight, select either:
- "Less Than" to format cells below a certain standard deviation.
- "Greater Than" to format cells above a certain standard deviation.

6. Formula bar: In the formula bar below the selection, enter the following formula (replace A1:A10 with your actual data range):

- For values below one standard deviation: `=A1 < AVERAGE(A1:A10)-STDEV.S(A1:A10)`
- For values above one standard deviation: `=A1 > AVERAGE(A1:A10)+STDEV.S(A1:A10)`

Explanation:
- `AVERAGE(A1:A10)` calculates the average of your data range.
- `STDEV.S(A1:A10)` calculates the standard deviation of your data range (use STDEV.P for population standard deviation if applicable).
- The comparison (< or >) checks the cell value against the average adjusted by the standard deviation.

7. Formatting options: Click on the "Format" button to choose how you want to highlight the cells (e.g., fill color, font color, etc.). Select your desired formatting options.

8. Click OK: Click "OK" on both the "Format Cells" and "New Formatting Rule" windows.

Now, your conditional formatting rule is applied. Cells with values falling below one standard deviation (or above, depending on your chosen rule) will be formatted according to your chosen style.

Additional Tips:

* You can create separate rules to highlight cells above and below different standard deviations (e.g., 1, 2, or 3 standard deviations).
* You can adjust the formula to target a specific number of standard deviations by changing the value after the plus or minus sign in the formula.
* Conditional formatting can be very flexible. Experiment with different formatting options to create clear visual distinctions for your data analysis.