There are two main ways to secure your workbook with a password in Excel:

Method 1: Encrypting the Entire Workbook

This method protects the entire workbook, restricting access to opening or modifying it without the password.

1. Go to File Info: Click the "File" tab and then select "Info" from the backstage view.
2. Protect Workbook: Look for the "Protect Workbook" section and click on "Encrypt with Password."
3. Enter Password: In the "Password to open" box, type your chosen password. Remember, choose a strong password that's difficult to guess and keep it safe (written down somewhere secure, not within the document itself).
4. Re-enter Password: Confirm your password by entering it again in the "Reenter password to open" box.
5. Save: Click "OK" to save your changes. Now, whenever you try to open this workbook, Excel will prompt you for the password.

Important Considerations:

* Microsoft cannot recover lost passwords for encrypted workbooks.
* Make sure you remember your password or store it securely.

Method 2: Protecting Worksheets (Optional)

While encrypting the workbook protects the entire file, you can also add an extra layer of security by protecting individual worksheets within the workbook. This allows authorized users to open the workbook but restricts them from making changes to specific worksheets without another password.

1. Select the Worksheet: Click on the worksheet tab you want to protect.
2. Review Tab: Navigate to the "Review" tab on the Excel ribbon.
3. Protect Sheet: In the "Protect" group, click "Protect Sheet."
4. Enter Password (Optional): If you want to restrict editing on this sheet, enter a password in the "Password to modify" box. Similar to workbook encryption, ensure it's a strong password and remember it well.
5. Grant Permissions (Optional): Click the "Select Cells" button to define what actions users can perform even with the sheet protected. You can allow users to select specific ranges, format cells, insert rows/columns, etc.
6. Click OK: Click "OK" to apply the password protection to the worksheet.

Remember: Even with password-protected worksheets, users can still view the content unless you encrypt the entire workbook using method 1.

By following these methods, you can add password security to your Excel workbooks and worksheets, safeguarding sensitive information.