In Excel, you can add comments to the current cell by one of two ways. You can either click the New Comment button on the Reviewing toolbar or choose Insert, Comment on the Excel menu bar. Excel responds by adding a comment box with your name listed at the top (or the name of the person who shows up in the User Name text box on the General tab of the Options dialog box). You can then type the text of your comment in this box. When you finish typing the text of the note, click the cell to which you're attaching the note or any other cell in the worksheet to close the Comment box.

Excel indicates that you've attached a comment to a worksheet cell by adding a red triangle to its upper-right corner. To display the Comment box with its text, position the thick, white-cross mouse pointer on this red triangle, or position the cell pointer in its cell and then click the Show Comment button on the Reviewing toolbar.