Excel Comment is basically short notes that can be inserted into any cell in Excel. You cannot see it if you do not click on the comment. It’s useful for reminders, notes for others, or for cross-referencing other workbooks.
Adding comment to worksheets cells are a great way to explain the cell contents, formulas, offer tips to users or other data in the spreadsheet.
Basically there are three ways to add a comment:
1) Using Menu bar
2) Using mouse right-click
3) Using Reviewing toolbar (not explain here)