Open the Excel workbook
Click the sheet you want to lock
Go to the Review tab
Click Protect Sheet
Enter a password if desired
Select the actions you want to allow
Click OK
Re-enter the password to confirm
Click OK
To lock the entire workbook, go to the Review tab
Click Protect Workbook
Choose the protection option
Enter a password if desired
Click OK
Save the file
To prevent editing by others, use File
Click Info
Select Protect Workbook
Choose Encrypt with Password
Enter a password
Click OK
Save the workbook again