So ignore the discussion on forecasting for now and concentrate on the theory of demand. The graphical relation between price and the quantity demanded, holding all else constant, is called the Demand curve.
Supply is the total quantity offered for sale.
The graphical relation between price and the quantity supplied, holding all else constant, is called the supply curve. Then, transform back to original model. When any of the other factors that influence demand change, the demand curve shifts. Higher indifference curves represent higher levels of utility. Suppose a consumer chooses a bundle of goods to maximize utility subject to his or her budget constraint.