the church is the highest and the most powerful on the feudal ladder. They got to tell the king what rules and laws to make.
the kings job is to make sure that the nation is running. He also gets to collect taxes and spend it however he wants. he is the second highest on the feudal ladder
the Nobles are land owners and will rent lands to knights when they want it. The benefits include having a good source of money and having to do little to no manual labor. He is third on the feudal ladder
the Knights job is to protect their lords and Nobels from threats and dangers and in return Knights were able to own their own land.
the serfs work the kings or nobles land farming and harvesting in return they got protection from dangers and land to work on and a house to live in.
Feudalism was brought by William the conqueror after he won the battle of Hastings. It was justified because the kings thought they where chosen by God. They maintained their power by building castles to control the population.