Step 1: Understanding the Law of Demand.
The law of demand states that, ceteris paribus, as the price of a good or service increases, the quantity demanded decreases, and vice versa. In other words, there is an inverse relationship between price and quantity demanded.
Step 2: Explanation with Diagram.
The law of demand is typically represented by a downward sloping demand curve on a graph where the x-axis represents quantity demanded and the y-axis represents price. As price decreases, the quantity demanded increases, which results in a negative slope for the demand curve. 
Step 3: Conclusion.
Thus, the law of demand shows that there is a negative relationship between price and quantity demanded, meaning that demand rises as prices fall, and demand decreases as prices rise.