Inserting comments in a cell becomes important when you want people to understand the purpose of a cell and what is the input it should have. It also helps in proper documentation.
In order to insert comments in a cell in excel, you can follow this procedure.
1) Select the cell where you want the comment to be added to.
2) Go to Review – New comment or you can just use the shortcut Shift +F2
3) You will see the comment box pop-up right next to the highlighted cell and the initial comment will be your system name. You can edit this and add your desired comment.
4) To modify the comment, you can just right-click on the cell and click on Edit comment.
This is how you can add a comment in excel. Also, do check out this website for some excellent MS Excel tutorials.