You have two main options to display a specific message if a cell is blank in Excel:

1. Using Conditional Formatting:

This method allows you to format the cell itself to display the message when it's empty. Here's how:

* Select the cell(s) where you want the message to appear if blank.
* Go to the "Home" tab on the ribbon.
* In the "Styles" group, click on "Conditional Formatting."
* Select "Highlight Cells Rules" and then choose "Blank cells" from the submenu.
* In the new window, under "Format style," choose the formatting you want for the message (e.g., font color, text).
* In the "Format values where this rule applies" section, you can enter your desired message in the text box next to "Format with."
* Click "OK" to apply the conditional formatting.

Now, any blank cell in your selected range will display the message you defined.

2. Using a Formula:

This method lets you enter the message in a separate cell and then use a formula in the target cell to display the message only if the original cell is blank. Here's how:

* In a separate cell (hidden or outside your main data area if desired), type your message (e.g., "Enter Data").
* Select the cell(s) where you want the message to conditionally appear.
* Enter the following formula in the selected cell(s), replacing `A1` with the actual cell reference containing the data you want to check for blankness:

`=IF(A1="", "Enter Data", A1)`

This formula uses the `IF` function. If the value in cell A1 is blank (""), it displays the message "Enter Data." If there's a value in A1, it displays that value itself.

Choose the method that best suits your needs. Conditional formatting directly applies to the cell itself, while the formula method offers more flexibility for displaying the message in a different location.