On a long solo car trip this past weekend, I downloaded several podcasts to listen to as the miles passed. One was a classic: The Invention of Money, originally released by NPR's Planet Money team back in January of 2011. I highly recommend listening (or re-listening) to it in full.
The podcast is a great reminder of how any currency in a monetary system is a fabricated construct. A simpler way to explain this is to say it has value simply because we believe it does.