To "protect" a spreadsheet, that is to say, to prevent unauthorized changes to the contents and formats of locked cells and to ensure that the contents of hidden cells are not displayed, follow these steps:
First, lock and hide the relevant cells (see Locking and hiding cells).
Next, select the Protect command from the Tools menu. The "Protect" dialog box is displayed.
Type in a password of your choosing. You will not see the letters; they are represented by asterisks to prevent anyone seeing your password accidentally.
Click on the OK button. You will be asked to re-enter your password.
The box will close and any locked or hidden cells will be unalterable until the Protect command is cancelled.
Unprotect the spreadsheet by selecting Unprotect from the Tools menu and entering the same password in the box. Locked and hidden cells will now be accessible again.
Note: You can protect a spreadsheet without entering a password. To do this, just click on the OK button of the "Protect" dialog box without entering a password. Obviously this is not a safe method, although it is an easy way to stop yourself altering cells you don’t want changed.
Write your password down in a safe place. If you forget your password, you will never be able to unprotect your spreadsheet!