Go back into your BIOS to tell your system to boot from the USB stick first.
Then, once it’s finished, simply plug it into your new system. Go back into your BIOS to tell your system to boot from the USB stick first. From there you can go through the prompts to install the operating system onto your new rig. Don’t worry about not having a software key during installation, you can activate Windows 10 once you reach the desktop.