I like starting all the way back in history. Humans transacted with social capital. It only works in situations with small numbers of people most of which are related in some way. This system worked for thousands of years. Eventually bartering was necessary and then the coincidence of wants became a problem. Abstract forms of money continued to evolve. This subject matter can get pretty deep but ripe for the picking. If you havent already listen to the Saylor series on the what is money podcast. Also, you might try diving into MMT as bizarre as it is. Look into the tally stick system. Examine the functions and properties of money. Hope this helps.