If the drive is just a raw un-initialized drive then just plug it in to the Mac and the Mac will ask you to either "Eject" this unrecognized drive or "initialize" it, choose initialize.If the drive is already initialized with another formatting utility then you need to mount it, go to the "Special" menu of the Mac, and choose erase disk. You may have to do this a couple of times. It should erase the disk and then install the Mac drivers on it. Some third party formatting utilities will also allow you to erase the drive so that the Mac will see it as "unrecognizable."