how do I insert comments per cell that reveal when the mouse hovers over the cell?

Hi Darren, Thank you for your post;
In answer to your question:

To Insert a Comment
1. Select the cell in which you want the comment.
2. Choose Insert>Comment
3. Type your comment where the cursor is flashing.
4. Text will wrap automatically. If you want to start a new line, press the Enter key.
5. When finished, click outside the comment box the comment will disply only when you hover your mouse over the cell which now has a red triangle in the top corner.

Just a few more things to do with Comments:

To permanently display a Specific Comment
1. Right-click the cell which contains the comment.
2. Choose Show Comment

To hide the comment:
1. Right-click the cell which contains the comment.
2. Choose Hide Comment

To Display All Comments
1. Choose View>Comments
Note: All comments in all open workbooks will be displayed.
2. To hide the comments, so they only show when you hover over the cell choose View>Comment again

To Format Text in a Comment:
You can change the font, the font size, font colour and font style, for all or part of a comment.
1. Right-click the cell which contains the comment.
2. Choose Edit Comment
3. To format all text, click on the border of the comment shape.
4. To format specific text within the comment, drag over the text to select it.
5. Use the Font tools on the Formatting toolbar to modify the text appearance
6. When finished, click outside the comment box.

Note: you can also change the shape of the comment box by using the Change AutoShapes command. (Some great shapes and styles can be created).

To Print Comments:
You can print comments as displayed on the worksheet, or print them at the end of the worksheet

To print as displayed:
1. Show specific comments or all comments.
2. Choose File>Page Setup
3. On the Sheet tab, from the Comments dropdown, choose 'As displayed on sheet'.
4. Click Ok
5. Choose File>Print (or click the Print button)

To print at the end of the worksheet:
1. Choose File|Page Setup
2. On the Sheet tab, from the Comments dropdown, choose 'At end of sheet'.
3. Click Ok
4. Choose File>Print (or click the Print button)

I hope that has answered your questions, regards Pete