Protection

By protecting a worksheet I assume you mean that you want users to be able to enter data in some cells but not enter or delete data in other cells which may contain formulas.

If you right click on a cell in a sheet and go to format cells- Protection tab by default all cells in a sheet are locked by default.

This lock on cells ONLY takes effect when the sheet is protected.

Now if you want to protect a worksheet to allow users to enter data in some cells but not in others

Highlight the cells that you want users to enter data in and right click and select format cells. Choose the protection Tab from the Format Cells dialog and uncheck the locked attribute for those cells. Unlocking the cells will have no effect UNLESS and UNTIL you select Protect sheet from the Review Ribbon.

When you click on Protect Sheet ensure
Protect worksheet and contents of locked cells is checked (this will ensure users cannot delete cells that are locked)

You can enter a password for sheet protection

Ensure also that users can select unlocked cells (otherwise they will not be able to type in the cells you want them to enter data in),

Check the other permission you want to grant to users of the worksheet.
Then click on OK to lock the sheet.

Thanks

Newson