To turn on placeholders in Excel, first open the Excel application. Then, click on the "File" tab in the top left corner of the screen. Next, click on "Options" in the drop-down menu. In the "Excel Options" window that appears, select "Advanced" from the list of options on the left side of the window. Scroll down to the "Display options for this worksheet" section and check the box next to "Show placeholders for empty cells." Finally, click "OK" at the bottom of the window to save your changes.
Now that you've turned on placeholders in Excel, you'll see a small green triangle in the top left corner of any empty cell. This triangle is called a placeholder, and it indicates that there is no data in that cell. Placeholders are useful because they make it easy to see which cells in your worksheet are empty and need to be filled in.
If you ever want to turn off placeholders, simply follow the steps above and uncheck the box next to "Show placeholders for empty cells."