Spengler views cultures as "organic" by which he means that the follow a life pattern, one he names by analogy to seasons. The spring of a culture is the time of the origin of its basic principles, the time of the birth of the religion of that culture. He believes that all great cultures have behind them a great religion. A culture acting "in form" (a comparison to athletes who are at the peak of their form) is in its summer, when all aspects can be seen as working under the principles at the basis of the culture, and when great accomplishments are made--the artifacts of lasting value.
Our culture, as compared to other cultures, is one of directedness and will; Spengler refers to it as Faustian. We see our religion as requiring us to convert others. Our art has a perspective, a point of view and direction. Our music is directed toward a tonal center. Our science is about forces and changes. We apply it to change our world. Our mathematics goes beyond the static geometry of the Classical world to deal with the calculus of tendencies and averages.
All cultures come to a Civilization, an autumn when this breaks down. Mega-cities are characteristic of this time. Politics is motivated by money, and move through Imperialism and the Period of Contending States to Caesarism, a period of despots. Science no longer reaches certainties. People no longer accept common principles or goals, they fight all rules from the past. The arts, rather than working in ways that seem obvious to the artists and the people, follow fashions with constant changes of style. Later in this culture after a period of atheism, people turn to a religious renewal based on the religion developed in the spring of the culture.
Spengler sees our culture as having finished its summer in about 1800--and with Wagner in music. He views developments in all the arts as evidence of decadence. His advice to those living in the Civilization phase is to look for the direction of movement and contribute positively to it--the Civilization will move in the direction of its Destiny, regardless of our choices. We can choose to contribute or to have no impact. "Either Will This, Or Will Nothing At All".