Simply put, money has one use: exchange. It is possible to trade without money, this is called barter. However, barter does not scale because without a unit of account the number of prices increases exponentially with the number of goods in the economy. An economy with only 2 good requires just one price, 3 goods 3 prices, 4 goods 6 prices, 5 goods 10 prices, 100 goods 4950 prices and so on ( n*(n-1))/2). A modern economy could never function without a medium of exchange to simplify this process and allow the prices to allocate resources. Prices contain information that allow individual to coordinate in a decentralized way.

There are 2 main principles that allow us to leverage trade to increase resources available for consumption. The first concept, specialization, is often attributed to Adam Smith. It is the very simple idea that if one focuses on a specific task or resource they are able to increase output by adding tools or other capital that would not be economical at a smaller scale. Another way of putting this comes from Austrian economist Bohm Bawerk. It is the idea that a less direct method of production can be undertaken to increase efficiency. This is often illustrated with the example of fishing: an individual could apply all their labour to try to catch fish by hand. Or a less direct route could be taken by first applying labour to constructing spears, fishing rods, nets, boats.

Secondly, Ricardian comparative advantage, often attributed to David Ricardo, is a less obvious but equally important concept. The essential point to comparative advantage is that even if one entity can produce more of good A and good B than their trading partner, that it can still be beneficial to both of them for them to trade. Consider the scenario where Alice can catch fish at a rate of 5 per day or collect coconuts at 15 per day. While Bob can only catch 1 fish a day or collect 5 coconuts. From Alices perspective 1 fish has a cost of 3 coconuts and 1 coconut costs her 1/3 of a fish. While from Bob's perspective a fish costs him 5 coconuts and a coconut costs him 1/5 of a fish.  Therefor if Bob focuses on collecting coconuts and Alice catches fish and they trade they are able to consume more fish and coconuts than had they not engaged in trade.

Money is the tool that allows individuals and groups of people to coordinate in ways that leverage specialization and comparative advantage.