Currency is a universal representation of trust created by humans. So much so that we don’t even ask why two pieces of paper with green, gold, and black ink is accepted as a medium of exchange for goods and services. One piece of paper can be exchanged for a cartful of groceries. Equally important, currency has enabled people to save the value of their labors for use at a future point in time.
Traditional currency we use everyday are issued by sovereign governments in which people base their trust and faith, in varying degrees.