Sometimes its important that idle fingers or malicious people don’t change your excel file, often one that is shared with a group or emailed around the office. Heres how to do it (I did it in Excel 2007)
1) Right click on the Sheet name at the bottom of the page.
2) Click the option to protect the sheet.
3) Ensure that all of the options are check marked and enter a password. (DO NOT FORGET THIS PASSWORD)
If someone tries to change the sheet they would need the password to do so. This way only the person with the password can ever modify the sheet.
4) When you need to edit it, you will have to use that password to unlock it. You can repeat these steps and instead of putting in a password, you can leave the password blank to unlock it later.