Hello,
NETVN82 has over 900 videos on YouTube, so I have no idea which one you referred to in order to review what you did.
What connection are you using to make the laptop monitor? Is the laptop serving as the only monitor or second monitor?
Here is the problem - video ports on a laptop are typically for video output only, not for video input. So I don't think it is possible to use it via a wired connection between computer and laptop.
However, depending on your hardware, your laptop can serve as a wireless display monitor, but in order to set it up, you need to be able to see, hence if the laptop is used as the only monitor, you will not be able to set this up as you cannot see where you are going.