Regular comments in Excel place a small indicator in the desired cell and require you to either mouseover the indicator or to use the Ribbon to view the comment. Some situations dictate that the comment appear when the cell is activated. by using Excel’s Data Validation, this can be easily done, just follow these instructions…
1. Select the cell that you want to attach the comment.
2. Go to the Ribbon and select the Data tab.
3. In the Data Tools section, click Data Validation.
4. In the Data Validation dialog box, select the Input Message tab.
5. Check the Show input message when cell is selected checkbox.
6. Enter a title for your comment in the Title textbox.
7. Enter the comment in the Input message box.
8. Click OK.
Now whenever that cell is activated, the comment will appear. When another cell is activated, the comment will disappear.