Insert the USB boot media into USB slot (Preferable One of the Back USB ports).
Power On your PC and press repeatedly F12 until boot manager appears on the screen.
ArkPC hardware is based on Gigabyte motherboards and boot manager option key is F12.
Booting from a bootable USB depends on motherboard manufacturer. Some manufacturers have different Key combinations for Boot Manager Option, you can try: TAB, ESC, F10, F12