Ask HN: Book for a layman on how money works, the history of currency?

Recently I had an embarrassing introspective moment where I realized I have no idea how money works. I vaguely feel that money is used to represent a valuable item such as gold that, in theory, the bank holds. But how does money work across countries? Who decides how valuable a currency is? What are the factors used in deciding that?

Can somebody recommend a book on the global economy for a total layman? I'm also interested in the history of it. How did the idea of currency take hold?

Thanks!