To protect cells in Excel, the general process involves locking the cells and then protecting the worksheet. By default, all cells are locked but that locking only takes effect once the sheet is protected. Here are the steps in detail:

1. Select all the cells (Ctrl + A).
2. Right-click and choose "Format Cells," then go to the Protection tab.
3. Uncheck the "Locked" box to unlock all cells if you want to protect only specific cells.
4. Select the cells you want to protect.
5. Right-click, go to "Format Cells," and check the "Locked" box for those specific cells.
6. Go to the Review tab, click "Protect Sheet," and set a password if desired.
7. Confirm the password and select what users can still do on the locked sheet.
8. Click OK to apply protection.

Once protected, only the locked cells are protected from editing, and the permissions specified for the worksheet are enforced. To edit the locked cells later, the sheet must be unprotected with the password if set. This method works for protecting all cells, specific cells, or even just the formula cells by initially unlocking everything and then selectively locking desired cells before applying sheet protection.