Scroll down until you find the Enable Code. I have no idea what flash device or whatever the guy was talking about. All I know, is that code is too long for any sane person to attempt to put it in.
A USB flash device is a USB drive hard disk that uses flash memory to store information. One of these could store Gameshark info far beyond what you could enter into a code input. I'd suggest you search a Gameshark site about information about how to properly store the codes on the device.