What is the explanation for the law of supply and demand?

How many shoes a company has and how many people want the shoes is demand. When the company has more than enough shoes, the supply is larger than the demand so the price is lower. When there aren't enough shoes, the demand is higher so the price is lower. For example, if there is only one dollar in the entire country, one person would be rich because they have all of the money. But if there was one trillion dollars, money would have less value because one dollar would only be 1/1,000,000,000,000th of all of the money.