Page 2 of my Basic Microsoft Excel training will review adding a comment to a cell and formatting cells.
A comment can be added to a cell for later reference; for yourself, or others. The comment is not seen on the spreadsheet as you review it, what you will see is a small triangle in the upper right corner of the cell denoting it has a comment associated with it. You could use a comment to denote how you arrived at the value contained in the cell or a note to another reader, so you can convey relative information in regard to that cell.
The format of a cell simply refers to what TYPE of information the cell contains, is it money, text, or a calender date? In order for the information to be displayed correctly you need to define it.
In this screen shot what we have done is left click on cell A5 to highlight it, then right click to bring up the menu.
Within the menu we see the two choices we are reviewing here. Selecting Insert Comment will immediatley bring up a small text box for you to type directly into. When you're done typing, click off in the field and the box will close. To delete the comment you merely need to right click on the cell, the menu will now contain that option.
Selecting Format Cells... will open the Format Cells box, typically on the "Number" Tab, there you will see your options for configuring the cell to manage your type of data correctly.