Comments in Excel

How to use comments in Excel worksheet 2007
You can add comments to an Excel 2007 worksheet cell to remind, provide certain instructions, maybe ask a question or other explanatory notes. For example, let’s say you have the name of students and the marks they obtained in the last examination. You can add comments like: Needs to improve in Maths or Needs help in English. The comment then pops up when the mouse cursor moves over the relevant cell. A cell with a comment has a red triangle in the top right corner. This alerts the user that the Excel cell has a comment.You can find the insert, edit and delete comment buttons in the ‘Review’ tab. You can show or hide the comments. You can also scroll through the comments in an Excel worksheet by clicking on the next or previous comment buttons. The text in the comment box can be edited using the standard editing procedures to change the colour of text, make it bold, change the font size, etc. You must, however, first select the text in the comment box.

Further reading:
Annotate a worksheet by using comments