With the breakup of the Caroligian Empire Europe slowly divided into a series of individual territories governed by great aristocratic families. Politcal power was local it was private and was passed from generation to generation. This is what is meant by feudal society.
To defend the feudal powers a new artistocracy came forth- the knighthood. They were responsible to the local lords. The lords would give the knight a piece of land and in return the knight would fight for his lord.
With feudalism went Manorialsim. This invovled the relationship between the peasant and the local lords. The free farmers needed defense, thus they surrendered themselves and their lands to the lcoal lord. In return he the peasant received protection. He was obligated to turn over a percent of his annual harvest to the Lord. The peasant slowly but surely became a serf and part of the lords permanent labor force.