How do I lock cells in Excel without the whole document becoming read only?

I suppose you want to lock certain cells instead of the whole sheets. To do that, choose the whole sheet, right click and then select "Format Cells", then "Protection", then uncheck the "Locked" option and click okay. Then select the cells you want to lock, right click and select "Format Cells", then Protection; this time, check the "Locked" option and click okay. Now go back to the main tab, select "Review", then click on "Protect Sheet", and do whatever you want to do with it. Now only the cells you "locked" are protected from editing instead of the whole sheet.