The Feudal System & the obligations of each class.
Basically, each class worked for the higher class. Obiously the lowest category is the Peasants. They got the worst treatment of all because they had to work very hard and did not receive much profit, if any, out of it. Their main purpose was to serve and survive. Above the peasants, were the knights. The knights were mainly military and the deal with them was that if they gave their service, they would gain protection, food, and shelter. Above the knights were the Lords, which were very important because they were right below the king and had a lot of power, which included getting the peasants and fief. Their main goals were to give the king loyalty and military aid so that nothing would happen to him. Sitting proud and high is the king who held most power. However, there was also a lot of power being distributed amongst the Roman Catholic Church, who could tax anyone, even if they didn't go to church and the loyalty/nobles had power.