It can be quite difficult for puzzling reasons. I bought my laptop with no OS because it was cheaper to buy a Windows license separately. I downloaded the ISO and put it on a USB drive and … It wouldn’t boot. It took me half a day and I had to follow guides with various black magic which I can’t even recall what was about to finally get the thing to boot from USB. After spending over a day on that, I installed Ubuntu and set up dual booting in about 30 minutes.