on the wiiu to uise a HDD you need an AC powered HDD or a USB y-cable
to use it on a PC just plug it in to a usb port and the computer should find it (it might as you to format)
after it is formated(it might not have a file system on it) it might work with the wiiU, it will need to be formated by the wiiU for it to work with the wiiU