Input Message

I have a spreadsheet with a table that uses a vlookup, I would like to have an input message, of instructions, that appears when the cursor is over a cell.
How would I do this?
Thank you for your help
Laura

Select the cell where you want the message to appear. From the menu bar select Data Validation.

Rules can then be set up to only allow a certain type of input (i.e Dates, Amounts or Custom - where you enter a formula) or if you want to allow anything leave the Allow box as anything. Select the Input message from the tab and enter the message you want to appear when the cell is selected and click on OK