There are two main ways to protect a worksheet in Excel from unauthorized changes:

1. Locking Specific Cells:

This method allows you to control which cells users can edit and which ones remain protected. Here's how to do it:

* Select the cells you want to protect: Click and drag to highlight the cells you want to prevent users from modifying.
* Format Cells: Right-click on any of the selected cells and choose "Format Cells" from the context menu. Alternatively, you can press `Ctrl+1` (Windows) or `Command+1` (Mac).
* Protection Tab: In the "Format Cells" window, navigate to the "Protection" tab.
* Lock the cells: Uncheck the box next to "Locked" if it's checked. This ensures these cells are locked.
* Apply Formatting: Click "OK" to apply the formatting changes.

2. Protecting the Entire Worksheet:

This method protects the entire worksheet structure, preventing users from formatting cells, inserting or deleting rows/columns, or hiding/unhiding elements. Here's the process:

* Review Tab: Go to the "Review" tab on the Excel ribbon.
* Protect Sheet: Click the button "Protect Sheet."
* Optional Password: You can add an extra layer of security by entering a password in the "Password to unprotect sheet" box. This password will be required to unprotect the worksheet and make any changes.
* Allow Users To: In this section, you can choose specific actions users are still allowed to perform on the protected worksheet. These might include selecting unlocked cells, using formatting options like font size or color changes, or inserting comments. Check the boxes next to the actions you want to allow.
* Click OK: Click the "OK" button to activate worksheet protection.

Important Notes:

* Remember the password you set for worksheet protection (if you used one). Losing the password can make it difficult or impossible to unprotect the sheet later.
* Locking specific cells is useful when you want certain data to remain fixed while allowing users to interact with other parts of the worksheet.
* Protecting the entire worksheet is beneficial when you want to restrict major modifications and ensure the overall structure remains intact.

By following these steps, you can effectively safeguard your Excel worksheets from unauthorized changes and maintain data integrity.