It's a visual representation of the law of demand. The demand curve can be a useful tool for businesses because it can show them the prices at which consumers start buying less or more. It can point out prices at which a company can maintain consumer demand and support reasonable profits.
Together with the law of supply, the law of demand helps us understand why things are priced at the level that they are, and to identify opportunities to buy what are perceived to be underpriced (or sell overpriced) products, assets, or securities.
The law of demand states that a higher price leads to a lower quantity demanded and that a lower price leads to a higher quantity demanded. Demand curves and demand schedules are tools used to summarize the relationship between quantity demanded and price.