windows boot disc/USB?

just built my first PC and am looking for a boot disc so I can install windows (assuming it powers up). i will be purchasing a legitimate key and am looking at 8.1 pro to upgrade to 10. thanks to the internet, however, I have choices.

I cannot make one from my current system because I'm still running xp.

name your terms. lunch. neighborhood cat (fixed!). bike riding lessons. hole digging. I am at your mercy.

edit: got what I needed, thanks y'all! fwiw, found a cheap 10N key, downloaded the 10N ISO, used RUFUS and the rest is history.