Comments

Ctrl + Shift + F2
Added in Excel 2016
Comments are short bits of text that can be used to explain calculations, assumptions or to provide reminders.
A comment is a bit of descriptive text that enables you to document your cells and formulas.
You can only attach one comment per cell although you can make the comments as long as you want.
Adding comments to your worksheet cells has several uses:
1) Useful for tracking progress and for tracing your footsteps when handling complex formulas.
2) Useful for reminding yourself how certain areas of a worksheet work.
3) Useful for communicating with other people when you are sharing the same worksheet.

Displaying Comments

To display a comment, use the mouse to hover over the particular cell.
You can set the show/hide of individual comments by right clicking and selecting show/hide comment.

Adding Comments

Selecting Comments

Editing Comments

Removing Comments

Formatting

To apply bold and other formatting effects to your comments select the text and press the right mouse button.
Select Format Comment from the shortcut menu
SS
If you want to remove the User Name from appearing you can remove it from (Tools > Options)(General tab, "User name").
Before you remove it completely be aware that this User Name is used in other places as well though.

You can format your comments so they look different from your colleagues.
Use the highlight tool on the Formatting toolbar to change the background colour of the comment.
Use the font tools to change the font attributes.

Printing

It is possible to print out all the comments on a worksheet. The page setup dialog box is worksheet specific.
Select (File > Page Setup)(Sheet tab).

At end of sheet - Prints the comments on an additional page.
As displayed on sheet - Prints the comments only if they are currently displayed on the worksheet.