Users need to be protected from themselves. None of us like to make a mess of things. It is handy to know that you can lock cells in a spreadsheet so that no one can type in them. You can do this by choosing Tools | Protection | Protect Sheet. By default, every cell is formatted so that that when you turn protection on, every single cell in the spreadsheet is locked. Try it — then try to type in a cell. You will get an error message.  Unprotect the worksheet.

What you really want is to have a group of cells so that users can type in those cells and those cells only. Select the cells you want open to the user. Choose Format | Cells | Protection and deselect the Locked option. Now protect the sheet again and you will find you can enter data into those cells and those cells only.