What is the principle of supply and demand?

Any potential producer of a product or a service needs first to determine the need for such goods. This is usually done through companies that do research by contacting either the public through surveys, or to specific companies that might require those services. They also inform you as to what other people or companies are also providing those services or goods, and if there is any available room in the market for a new comer. This then determines demand. This also determines the available supply to fill the demands. It is much like water always attempting to find equalibrium.