To use the Windows 10 Media Creation Tool, follow these steps (this tutorial focuses on downloading ISO and creating DVD or USB media for Windows 10):

A valid Windows product key is required when directly installing Windows 10 for the first time on a device.

The free Windows 10 license with permanent activation also applies to computers upgraded to Windows 10 final RTM Build 10240 from Windows Insider Preview Builds and pirated copies of Windows managed to trick Microsoft into believing it’s genuine. No product key is required (by skipping the product key entering) when clean install Windows 10 from scratch on a device which has previously upgraded to Windows 10 and gets activated in the past (hence the HWID, the hardware ID, is recorded on Microsoft activation server).

No product key is required when upgrading Windows 7 or Windows 8.1 that is genuine and activated to Windows 10.

No product key is required to download the Windows 10 ISO images, or to create DVD or USB media trough the Media Creation Tool.

Win 10 usb dvd download tool