Complex sentence: Serfs who occupied a plot of land were required to work for the lord of the manor who owned that land, and in return were entitled to protection, justice and the right to exploit certain fields within the manor to maintain their own subsistence.
Split into simpler sentences: Serfs who occupied a plot of land were required to work for the lord of the manor who owned that land. In return they were entitled to protection, justice, and the right to cultivate certain fields within the manor to maintain their own subsistence.