How to Unlock Bootloader on Nexus 6P
Make sure you have setup ADB and Fastboot environment on your PC.
Power off your device and keep it unplugged from your PC.
Boot into bootloader or fastboot mode. To do so, press and hold volume down and the power button for 5-6 seconds.
You will see the bootloader screen. Now plug in your device to the PC using a USB cable.
Navigate to the location where your ADB and fastboot is installed. While the folder with ADB and fastboot files is open, right-click on an empty space and select “Open command window here” option to launch a command prompt window.
Now check your fastboot connection by issuing the following command. It should return your device’s serial number. Otherwise, you need to make sure your drivers are installed correctly.
fastboot devices
Once you’ve confirmed your fastboot connection, issue the following command to unlock the bootloader.
fastboot oem unlock
Now you should see a message asking you to confirm this action. Use the volume keys to scroll and the power key to confirm.
Once the process is done, issue the following command:
fastboot reboot
Now you can disconnect from your PC once the process completes.
Now your device is ready for further development. You can install a custom recovery and also root your device. You can check the ADB connection of your device by issuing the “adb devices” command in cmd. For any queries, comment down below.