People who are trying to make money by selling groceries, or cars, or computers, or machines that make cars and computers, need to know what consumers want and how much they would be willing to pay. It's not in a massive book. Prices This vitally important information about other people's wants is embodied in prices. Prices don't just tell us how much something costs at the store. The price system pulls together all the information available in the economy about what each person wants, how much he values it, and how it can best be produced.
Prices make that information usable to producer and consumer.
Each price contains within it information about consumer demands and about costs of production, ranging from the amount of labor needed to produce the item to the cost of labor to the bad weather on the other side of the world that is raising the price of the raw materials needed to produce the good. Market prices tell producers when something can't be produced at a cost less than what consumers will pay for it. Every use of time or other resources to produce one good incurs a cost, which economists call the opportunity cost. That resource can't be used to produce anything else. The information that prices deliver allows people to work together to produce more.