MightyPinecone: For a while (the offer ended 2016-07-29) W10 was free if you already had W7, W8, or W8.1 on your computer. Now you do have to buy a license, however. Or buy a new computer and have the license cost included in the price of the computer.
Regarding installation using the Windows 10 installation media:
"Yes, the media creation tool and Windows 10 installation media (ISO files) are available for customers to install Windows 10. If you’re installing Windows 10 for the first time, you’ll need to enter a valid Windows 10 product key or buy a full version of Windows 10 during setup for this tool to work. If you’ve previously installed Windows 10 on your device, you should have a digital license and Windows 10 will automatically activate without entering a product key. " (
Source)
It's still free for Windows 7 or 8.1 users.
When setup asks just type your product code from either 7 or 8.1 when doing a fresh install. If you're upgrading in place (running Windows 10 setup from within either 7 or 8.1) then just click I don't have a code if it asks for one, and it should activate fine.
If your on 8, then you can upgrade to 8.1 for free then upgrade to 10 for free, but you NEED 8.1 you can't just go from 8 to 10.
Also when you do a fresh install from an upgrade in the future you can just install 10 straight (you don't need to install your older one) when it asks for a product code just say I dont have one, and it will activate fine. (Its just the first time you install 10 from an upgrade you need it.)