By default all cells in a worksheet are locked when sheet protection is
enabled.
It is up to you to decide which are to be locked or unlocked when the sheet
is protected.
Format>Cells>Protection is where you would change the "locked" or "unlocked"
status.
CTRL + a to select all cells and unlock them.
CTRL + click to select the cells to be locked and lock them
Then Tools>Protect>Protect Sheet.......add a password if you wish but these
are easily broken and will not stop a savvy user.
Note the selectable options under "allow users to" when protecting,
Gord Dibben MS Excel MVP