I need help making a Windows 10 boot-drive

[SamLindler97]

So, I bought a PC back in 2015 with Windows 8.1 because I knew I'd upgrade to Windows 10 for free.
Here I am upgrading my motherboard and CPU and I'm needing to make a Win10 bootable with a USB. I have a blank 16GB USB but I just want to make sure I'm able to do this since I didn't actually buy Win10. I seen a video that said I needed to download some 3rd party software to get a 'key' to enter once I'm setting up Win10 on the new system...
This is my first time actually upgrading my PC and I feel like a lost pup...

 

[Rocky Bennett]

You do not need a key, that was WAY back in the old days. All you need is an image downloaded straight from Microsoft https://www.microsoft.com/en-us/software-download/windows10ISO

and a tool to create a bootable USB stick. Rufus is easy and popular

https://rufus.akeo.ie/

You might want to read this article;

https://www.howtogeek.com/226510/how-to-use-your-free-windows-10-license-after-changing-your-pc%E2%80%99s-hardware/