Banks and money

All values in the economic system are measured in term of money.
Our goods and sold for money, and that money is in turn exchanged for other goods and services.
Coins are adequate for small transaction, while paper notes are used for general business.
There is additionally a wider sense of the word «money», covering anything which is used as a means of exchanged, whatever form it may take.
Originally, a valuable metal (gold, silver of copper) served as a constant store of value, and even today the American dollar is technically «backed» by the store of gold which the US government maintains.