In medieval times, the house that the local lord lived in was called the manor house. The manorial system gets its name from that. The person living in the manor house (the local lord) was tasked with protecting the people in the local village. In exchange, the people in the village made sure the noble had all the food and anything else he might want for himself or his family. Together, the lord and the village made up a unit called the manor. This system of protection for provision was called the manorial system.
The manor was the lowest building block in the pyramid of the feudal system. At the very top was the king. The local manors were at the very bottom.
The local lord or noble was pledged to protect his village. He was also pledged to help the noble above him. Many manors were pledged to the same noble. A group of manors could combine forces and be led by the noble above them in order to protect their people from attack.
Medieval times were violent times and people did need protection from bandits and wars. Peasants barely had enough time to grow crops. They did not have time to learn how to fight as well, so they needed someone who knew how to fight to protect them.