A classic example of an interface are the buttons on a vcr/dvr/etc.
Play, Stop, Rewind, etc all cause something similar.
But on a VCR rewind means physically spinning a motor backwards. On a DVR it means moving a laser towards the center..
You don't need to know how it works, just what it does.
Then, as technology advances, you can always still call play, and you just swap in a different implementation, and all other code remains the same






