An external drive is a portable storage that can be connected to your Mac using a connecting cable. For connection, you need to attach the external drive with a power source with one end. Now connect the other end with an open USB or Firewire port on your computer. Now click “Finder” on the dock and click on the “Application” folder. Click on “Utilities” now click “Dick Utility.”  Now click the option and go to “Guide Partition Table” (or Apple Partition Map). Click on Partition. Once the process is complete, you can transfer data to/from the device to your Mac.