You can lock a computer in several easy ways, especially on Windows systems. Here are the most common methods to lock your computer screen securely:

1. Use the keyboard shortcut: Press the Windows key + L simultaneously. This instantly locks your computer and brings up the lock screen requiring a password or PIN to unlock.
2. From the Start menu: Click the Start button (Windows logo) at the bottom left of the screen, then click your user profile icon, and select Lock from the dropdown menu.
3. Using Ctrl + Alt + Delete: Press Ctrl + Alt + Delete together, then choose Lock from the options that appear on the screen.
4. Via Command Prompt: Open Command Prompt and type the command Rundll32.exe user32.dll,LockWorkStation then press Enter to lock the computer.
5. Automatic locking with Dynamic Lock (Windows 10/11): You can pair your Bluetooth device such as a smartphone to your PC, and your PC will automatically lock when the paired device moves out of range.

On macOS, common shortkeys like Control + Command + Q also quickly lock the screen. Locking your computer does not close your applications but just secures your session, requiring a password or PIN to regain access. The quickest universal way to manually lock your Windows PC is to press Windows key + L on your keyboard.