S67675 :
http://www.tenforums.com/tutorials/2376-usb-flash-drive-create-install-windows-10-a.html
How to Create a Bootable USB Flash Drive to Install Windows 10
One more question about windows 10 is a product key needed or not (for a new pc)
Well it's not needed to get Windows 10 installed, but you'll need one to make Windows 10 activate and make it legitimate.
That is unless you have a Windows 7 / 8.1 Product Key that is tied to your system already. With the latest version of the installer, MicroSoft allowed uses to do a clean install immediately rather than the upgrade followed by a clean install which was required before. So if you are doing a clean install on a computer that already has a legitimate product key for Windows 7 / 8.1 then when asked you enter that product key during the install process and when Windows activates it will use your old product key to check against your hardware (to check that it belongs to that computer) and if everything matches up you are given your Digital Entitlement.
However since you've said that you have a new system, you don't qualify for a Digital Entitlement.