Inserting a tally mark in Excel is quite simple. Here are the steps:

1. First, select the cell where you want to insert the tally mark.
2. Next, click on the "Insert" tab in the ribbon at the top of the screen.
3. From the "Symbols" section, click on the "Symbol" button.
4. In the "Symbol" dialog box, select "Wingdings" from the "Font" dropdown menu.
5. Scroll down until you find the tally mark symbol (it looks like a vertical line with four diagonal lines crossing it).
6. Click on the tally mark symbol to select it, and then click on the "Insert" button.
7. The tally mark symbol will now be inserted into the selected cell.

Alternatively, you can also use a keyboard shortcut to insert a tally mark. Here's how:

1. Select the cell where you want to insert the tally mark.
2. Press the "Alt" key on your keyboard.
3. While holding down the "Alt" key, type
   Formula:

   "0251" 

   on the numeric keypad (make sure Num Lock is on).
4. Release the "Alt" key.
5. The tally mark symbol will now be inserted into the selected cell.

That's it! You can now use these methods to insert tally marks in Excel whenever you need them.