When sharing your spreadsheet with other users, you don’t want them to modify some specific cells. These cells may contain key data, instructions, statistics, or formulas. So, you can lock these cells in order to protect them.
Unlock all Cells:
It turns out that by default all cells are locked for editing in a spreadsheet, but it has no effect until you protect the worksheet. So, first, you need to unlock all cells, by following these instructions
Step 1: Press CTRL+A (To select whole range of sheets).
Step 2: Right click, then click on Format cells option.
Step 3: Choose the Protection Tab (Alternatively press CTRL+1).
Step 4: Untick the locked option and click OK.
Locking Specific Cells:
Now that you have unlocked all cells, you can go ahead and lock specific cells.
Step 1: Select cells that you want to lock.
Step 2: Press CTRL+1.
Step 3: Select Locked option and click ok.
Protecting the Worksheet:
Locking the cells has no effect until you protect the worksheet. Note following steps-
Step 1: Go to Review tab.
Step 2: Click Protect Sheet.
Step 3: Choose a password and click OK.
Now, with the sheet protected, users will not be able to edit locked cells. If they try to, they will get an error message.