To protect your Excel workbook with a password, you can follow these steps:

1. Open the Excel workbook you want to protect.
2. Click on the “File” tab in the Excel menu.
3. In the “Info” section, click on “Protect Workbook” or “Protect Workbook Structure” (the wording may vary depending on your Excel version).
4. From the drop-down menu, select “Encrypt with Password.”
5. A dialog box will appear asking you to enter a password. Choose a strong password that is not easily guessable but is memorable to you. Make sure to remember the password, as it cannot be recovered if forgotten.
6. After entering the password, click “OK.” A confirmation dialog will appear asking you to re-enter the password.
7. Re-enter the password to confirm, and click “OK.”
8. Save the workbook. From now on, whenever someone tries to open the workbook, they will be prompted to enter the password.

It’s important to note that while password protection can provide a level of security, it is not foolproof. There are tools available to crack or bypass Excel passwords. Therefore, it’s a good practice to combine password protection with other security measures if your workbook contains sensitive or confidential information.