How to create a drop-down list using the DATA VALIDATION function in Google Sheets?

To create a drop-down list using the DATA VALIDATION function in Google Sheets, you can follow these steps:

1. Open your Google Sheets document.
2. Select the cell or range of cells where you want to create the drop-down list.
3. Click on the 'Data' tab in the menu bar.
4. Click on 'Data validation' in the dropdown menu.
5. In the 'Data validation' window that appears, select 'List of items' from the 'Criteria' dropdown menu.
6. In the 'List of items' field, enter the values you want to include in the drop-down list, separated by commas. For example, if you want to create a drop-down list containing the options "Option 1," "Option 2," and "Option 3," you would enter "Option 1, Option 2, Option 3".
7. Optionally, you can choose to 'Show dropdown list in cell' by checking the corresponding box.
8. Click on 'Save' to apply the data validation and create the drop-down list.

Now, the selected cell or range of cells will have a drop-down arrow next to it, and when you click on it, you will see the options you entered in step 6.

Note: The data validation will prevent users from entering any other values than the ones in the drop-down list.