On the Protection tab of the dialog box Cell you can prevent cells from being changed, to hide the cell content or formula, or to disable printing.
Open the dialog box by clicking on the group arrow
in the bottom right corner of the ribbon tab Home | group Alignment (or group Number). Switch to the Protection tab.
Alternatively, open the dialog box by right-clicking on the selected cells for the context menu and select the Cell entry.
For more information, see Sheet protection.