Summarize this article in one sentence.
Most hard drives connect via USB, so you'll just need to plug the USB cable into an open port on your Mac. You'll typically find at least one USB port along each side of the Mac. Some Mac-specific drives may come with a Thunderbolt or FireWire cable instead. If this is the case, you'll need to plug it into the correct port, or get an adapter if you don't have the proper port on your Mac. If the drive is formatted and connected properly, it will appear on your Mac's desktop as a drive with a USB or Thunderbolt icon.  The drive icon may not appear on your desktop even though it is connected properly. You can check for the drive in the left frame of any Finder window, under the "Devices" heading. You can set drives to appear on your desktop by clicking the Finder menu, selecting "Preferences," and then checking the "External disks" box.  If the drive does not appear in Finder or on your desktop, see the next section. Double-click the drive on your desktop or select it from the left frame of a Finder window to view the contents of the drive. You can start dragging and dropping files into the drive, or copy files to your Mac's internal hard drive.

Summary:
Plug the hard drive into the Mac using the cable that came with it. Check for your drive on your desktop. Open the drive to view its contents.