Add Comments to Formulas and Cells in Excel 2013
 

When entering formulas in Excel, you may want to remind yourself, or someone else, what it was for in the future. Or you may want to add instructions to let users of your spreadsheet know what to do in certain cells.

We will show you how to add a comment to a formula and a comment that displays when you move your mouse over a cell.

http://www.howtogeek.com/162231/add-...in-excel-2013/