All the cells in a worksheet are locked by default so if you haven't unlocked any cells, then they are already locked. If you want to prevent anyone form changing the formulas but allow them to enter data in those cells without formulas, then you have to unlock the cells without formulas. You can do this one cell at a time or by selecting a range of cells, right clicking on any of the selected cells and click 'Format Cells', click the 'Protection' tab and uncheck the 'Locked' box. Then you protect the worksheet with or without a password by clicking the 'Cells' group in the 'Home' tab at the top, then click 'Protect Sheet'.