How to explain a demand and supply graph for a certain good or service

Assuming that all the goods in the market are identical, thus sold for the same price, that the information is freely accessible to everyone and that every other factor, a part from supply and demand, remains constant, the graph above shows a perfectly competitive market for good X.

At equilibrium the quantity supplied (Q_S) and the quantity demanded (Q_D) are equal (Q_S=Q_D=Q’) and the price (P’) is set by the market. Consumer surplus is the difference between what consumers are willing to pay for a good and the amount they actually pay for it. Producer surplus is the difference between what producers are willing to accept in exchange for their good and what they actually receive for it. Furthermore, assuming that the marginal utility of income remains constant, that is if the value of money for consumers remains constant, we can represent consumer and producer surplus as two triangles. The former delimited under the demand curve and above the market price and the latter delimited below the market price and above the supply curve. The total economic welfare that producers and consumers gain by participating in the market is represented by the sum of the two triangles.

(This answer would be accompanied by a graph and, if the student required so, by an in depth discussion of the economic concepts cited in the answer)