The highest person in the Feudal system is the King and he controls everyone and the only person that is higher than the King is God and the King is a vassal to God.
I am a Knight and I serve for my lord
Another thing about the King was many and most all people at the time believed in what is known as the Divine Right Theory which is that God chose the King and that you should treat the King very good or else.
I am a Serf and I work and serve everyone
The next person below the King on the Feudal System is the lord and the lord prepares armies for the King to protect him if attacked. The lord is a vassal to the King and is like a servant to the King.
We are serfs and we are given land to work on
The next person below the lord in the Feudal System is the Knights and the Knights fight in wars and battles for their lord and for the King. Knights are a vassal to their lord and serve for their lord by protecting.
On the very bottom of the Feudal System below the knights was the Serfs or also known as peasants. The peasants did all the hard work like farming and working outside all day and doing all the hard work on the land. The Serfs were a vassal to everyone and served everyone from the King to the lords and also the knights.
Serfs were given land also known as fiefs to farm and plant on to have food and also had to care for the land and they had to work on the land all day and everyday. Serfs were also poor and their kids and family would most likely be Serfs and be poor as well because only the people with money could have their children and family become higher ranked on the Feudal System or be able to become a knight.