Synthetics are "pure" oils designed to excel at extreme temperatures. Regular oils are mineral-based: they come from crude oil that is taken out of the ground and run through a refinery. Synthetics, on the other hand, are man-made in a chemical plant. They tend to be more consistent in viscosity over various temperatures.
While synthetics can improve your engine performance, they don't eliminate the need for regular oil changes. Synthetics can handle heat better than regular oil, but additives can only work for so long and the engine will still contaminate the oil.