Here's how to use data validation to restrict data entry to a specific range of values in Excel:

1. Select the cell(s): Choose the cell(s) where you want to limit data entry. You can select a single cell, a range of cells, or even multiple non-adjacent cells.

2. Data Validation: Navigate to the "Data" tab on the Excel ribbon. In the "Data Tools" group, click "Data Validation."

3. Settings Tab - Allow: In the "Settings" tab of the Data Validation window, under the "Allow" dropdown menu, choose the option that best suits your restriction:

* Whole number: Only whole numbers (e.g., 1, 2, -5) will be allowed.
* Decimal: Only decimal numbers (e.g., 3.14, -1.25) will be allowed.

4. Settings Tab - Data (for range): If you want to restrict the data entry to a specific range, here's what to do:

* Between: Choose "Between" from the dropdown menu under "Criteria."
* Minimum & Maximum: In the "Minimum" and "Maximum" boxes, enter the lower and upper limits of the acceptable range, respectively. For example, if you only want values between 10 and 20, enter 10 in the "Minimum" box and 20 in the "Maximum" box.

5. Input Message (Optional): In the "Input Message" tab, you can type a custom message that will appear when users select the cell. This message can explain what kind of data is allowed in that cell.

6. Error Alert (Optional): In the "Error Alert" tab, you can customize the message and style of the alert that appears if users try to enter invalid data.

7. Click OK: Once you've defined your settings, click "OK" to close the Data Validation window.

Now, when users try to enter data into the selected cell(s), Excel will only allow values that fall within the specified range. If they enter an invalid value, they will see the error alert message you created.