When you lock a computer, it protects it from unauthorized use when you need to step away from the PC, and don’t want to sign out or shut down.
Starting with Windows 10 build 15031 (8th Feb. 2017), Microsoft officially introduced the Dynamic lock feature that allows Windows 10 to detect when you’re away and automatically lock the device.
If you forget to lock your PC or tablet when you step away, Windows Hello can use a phone that is paired with your device to automatically lock it shortly after you’re out of Bluetooth range. Take your phone with you when you move away from your PC, and it will automatically lock a minute or so after you are out of Bluetooth range. (Note that Bluetooth range varies by devices.)
This tutorial will show you how to automatically lock your Windows 10 PC with your phone using Dynamic lock.