Here are the steps to lock cells in Excel:

1. Select the cell or cells you want to lock.
2. Right-click on the cell selections and select "Format Cells".
3. Click on the "Protection" tab.
4. Place a checkmark next to the field labeled "Locked".
5. Click OK or Cancel.

These steps will lock the selected cells in Excel. If you want to lock all the cells in a worksheet, you can follow these steps:

1. Click the Review tab.
2. In the Changes group, click on Protect Sheet.
3. In the Protect Sheet dialog box:
- Make sure that you’ve checked the box ‘Protect worksheet and contents of locked cells’ (it’s checked by default).
- Enter a password (if you want to password protect the sheet).

If you want to lock only specific cells in a worksheet, you can follow these steps:

1. Select the cells that you want to lock.
2. Click on the dialog box launcher in the Alignment group within the Home tab (or use the keyboard shortcut Control + 1).
3. In the Format Cells dialog box, in the Protection tab, check the box for Locked.