Select the entire worksheet by clicking the triangle at the top-left corner or pressing Ctrl+A
Right-click and choose Format Cells
Go to the Protection tab
Uncheck Locked and click OK
Select the cells you want to lock
Right-click and choose Format Cells
Go to the Protection tab
Check Locked and click OK
Go to the Review tab
Click Protect Sheet
Set a password if needed
Click OK
Only the selected cells will be locked after sheet protection is enabled