To create a Drop-down List, each distinct option is entered in the Source box in the Data Validation dialog. The items should be separated by a:

To create a drop-down list in Excel, each distinct option that you want to appear in the list needs to be entered into the Source box in the Data Validation dialog. The items should be separated by a comma.

For example, if you want your drop-down list to include the options "Option 1", "Option 2", and "Option 3", you would enter them in the Source box as follows:

Option 1, Option 2, Option 3

This method allows users to select from predefined choices, thereby minimizing entry errors and standardizing inputs. It's a practical feature for data entry in forms, spreadsheets, and various administrative tasks in Excel, ensuring that only valid entries can be made and making the data collection process smoother and more efficient.