Supply and demand curves are important curves in economics, and in other relevant fields. I am giving a link where the graph is available which is very important to understand the behavior of demand and supply. Demand curve is usually downward sloping which means that with the increase in the prices of the products, quantity demanded of the products is decreased. This means that price and quantity are inversely related with each other. On the other hand, supply curve is upward sloping because when prices are increased then demand decreases and excess supply is produced in the economy. In this way in the demand and supply diagram, demand is downward and supply is upward sloping.
Diagram
Diagram