You don't need a Mac to install Windows on a PC. I'm sorry I am not understanding your issue.
Buy Windows 10 (USB, Disc, or Digital Key) .
If using a USB or Disc that is then shipped to you, you would insert the media into your PC and restart the computer. You will be prompted to boot into the Disc or USB, at which point you follow the Windows Installation instructions to install the OS on your new PC.
If you just want to buy a digital key and have a USB drive of your own handy, you can download the Windows 10 installer from the Windows website
You probably should ask how to install Windows on a Windows Help Forum.