The buyer represents the demand side of the market. Every rational buyer aims at maximizing his satisfaction by purchasing more at a lower price and less at a higher price. This is called demand behaviour of a buyer i.e. law of demand. The seller represents the supply side in the market. Every rational seller aims at maximizing his profits by selling more at higher a price and lesser at a lower price. This is called supply behaviour of a seller i.e. law of supply. The objectives of consumers (buyers) and firms (sellers) are opposed to each other. This leads us to examine the actual price charged and quantity sold in a particular market.
There is only one price at which the objectives of sellers and buyers meet together. At that point, the quantity of a commodity demanded by the buyer is equivalent to the quantity that the seller is willing to sell. This price is called the equilibrium price and it occurs at the point of intersection of the supply curve and the demand curve.