Here are the steps to lock specific cells in Excel:

1. Select the cells you want to lock.
2. On the Home tab, in the Alignment group, click the small arrow to open the Format Cells popup window.
3. On the Protection tab, select the Locked check box, and then click OK to close the popup.
4. If you want to protect the worksheet, do the following:
- On the Review tab, click Protect Sheet (in the Changes group).
- In the Protect Sheet dialog box, select the options that you want.

That's it! The selected cells are now locked and protected. If you want to unlock them later, just follow these steps again and uncheck the Locked check box.