There are a few ways to lock your screen. You can do any of the following:

1. Press the Windows Key + L.

2. Simultaneously press Ctrl + Alt + Del and click "Lock" or "Lock this computer" when the screen appears.

3. Windows 7: Click the Start Menu. At the bottom of the Start Menu you will see a Shut down button with an arrow to the right of it. Click on the arrow and a submenu will open. Click "Lock."

4. Windows 10: Click the Start Menu. You will see a profile of a person on the left-most side, above a gear and a power button. Click the Person, then click "Lock."