Downloading Windows to Install it
For a number of years now Microsoft Windows has been available as a download that you can "burn" to a DVD or a USB drive and use to install a fresh copy.
Of course, there's often a catch.
Finding old operating systems to download WITHOUT viruses and rubbish attached is tricky.
Windows 10 is available from Microsoft itself but often we don't want to use the method we are forced to use when we get there.
Microsoft force their downloader on you and getting an ISO image after that has a couple of extra steps that have the potential to screw new players.
So here's how to download the ISO image directly, from Microsoft, ...but there's still a catch.
We have to trick Microsoft into doing it. It is a white lie. I am pretty sure that is OK.
The details of how to do this are outlined at this web site: https://www.howtogeek.com/427223/how-to-download-a-windows-10-iso-without-the-media-creation-tool/
Once you have you ISO image you just have to learn how to make a bootable DVD or USB thumb drive and then boot up your soon-to-be-a-fresh-windows-10 pc using that media.
Have fun with that :-)