Feudalism was the way people lived in the Middle Ages. There was a king, who gave land to his nobles in return for their loyalty. The land came with peasants, or serfs, who were the majority of the population.
No, the black death did not end the middle ages. The black death caused a lot of changes, some important, such as causing members of the nobility to try to tempt serfs to move onto their land and away from the land they were bound to. But the middle ages continued for another hundred years or more.
The "serfs" in the middle ages where people who were poor. They were basically born into slavery similar to some black slaves. They were allowed to own their own land sometimes. They had to stay on their masters land and payed to use their material.