How it works
About a thousand years ago in China, people paid with copper coins on strings. A merchant needed many strings, and they were heavy.
Merchants left their coins with a shop they trusted, and the shop gave back a paper note. A friend of the shop swapped the note for coins in the next city.
Later the government printed notes with carved wooden blocks. A note had a picture and a seal.
People trusted a note because they could swap it for coins. Paper is light.