What Is The Difference Between Demand And Supply And What Effect Can It On The Standard Of Living?

Demand is the will of consumers to buy a good or service provided they have the ability to purchase it. Supply on the other hand is the amount of goods and services suppliers/producers are willing to produce and sale at a given period of time.
Demand is inversely proportional to price. The more expensive something is, less people are going to want to buy it. Supply, however, is directly proportional to price. A higher price shows the producers a chance to gain more profits. So, they increase their production in hopes that more people would buy a product if more of it is in the market and so, they will gain higher profits.
About standard of living, it is obviously going to be higher if prices are lower (and hence, demand is higher). Actually demand and supply exist in an equilibrium known as market equilibrium* where the amount supplied is the amount demanded. So, all the forces that determine demand and supply eventually equal out at equilibrium. The higher up the equilibrium point is, the more is the standard of living.

*If you plot both the graphs of demand and supply together, the point at which they intersect is the equilibrium point.