New To Computers, I need help with Understanding Windows 10

So you can create a Windows 10 flash drive and install it without a license with the Media Creation Tool: https://www.microsoft.com/en-us/software-download/windows10

However, because you're using it unlicensed there will be some features you're locked out of in Settings, plus you'll have the annoying watermark on the bottom-right. You'll still have the basic stuff you need like internet access of course, so if you're concerned about also paying for Windows, you could always build the system now, install Windows unlicensed, then purchase a license later on when you've built up some funds again.