Presumably bartering came first. Who first thought of using money (coins and/or notes) of specific denominations, and on what basis was its worth decided upon?
To use a relatively recent example, when was the US dollar created, and what was used before its invention? When America was originally colonized, did the immigrants use the money from their countries of origin? How was the original dollar valued?
After coinage became commonplace, how were exchange rates worked out? For example, when rich young Englishmen did the continental tour in the eighteenth century, did they take English pounds (£) with them? Did the Italians, for example, convert them, and, if so, on what basis?
When countries colonized other countries, did their currency supplant the indigenous one?
Basically, how does money originally find its value, and how was money first traded?