It makes sense to add instructions for the spreadsheet user right there in the spreadsheet. Why go to all the trouble of creating an electronic spreadsheet and then also creating a paper-based instruction sheet? This only adds to the photocopying bill for no real gain. Excel allows you to insert a comment into a cell. When the user puts their mouse on the cell, the comment appears as a side box.

Try it. Go to a cell. Click Insert | Comment and type some text in the comment box.  Change the size of the comment box by using the handles.

To edit a comment, click the cell with the comment and choose Edit | Comment.

You can change the font size, type and colour and the size of the comment box.  Select the text and change the font properties in the usual way.

You can change the properties of the comment box itself.  Click the cell with the comment and choose Edit | Comment.  When the comment box appear, click on the border of the comment box and change the fill and border by choosing the fill colour and line colour tools on the drawing toolbar.

Add any other comments to the spreadsheet that you deem useful.