The Normans introduced the French language and traditions. Feudalism, wich already existed to some extent, was grealty developed.
Under the feudal system the king was the owner of all land, but this was then held by others, called vassals, in return for goods and services, espercially military service of about forty days a year. The chief vassals, the barons, received land from the king, and then created other vassals, the Knights and the villains.
The peasants could be villains, who were free but attached to the land on which they were born (the right to the land was passed on from father to son), or serfs, who were almost slaves. While the knights gave military service to his lord in exchange for his land, the peasant's service was in the form work on his lord's farm.
The Feudal Society