By default, all cells are locked. However, locking cells has no effect until you protect the worksheet.
1. Select all cells.
2. Right click, and then click Format Cells (or press CTRL + 1).
3. On the Protection tab, you can verify that all cells are locked by default.
4. Click OK or Cancel.
5. Protect the sheet.
All cells are locked now. To unprotect a worksheet, right click on the worksheet tab and click Unprotect Sheet. The password for the downloadable Excel file is "easy".