A system of living together for safety reasons. Parts of a manor include a large castle, a workshop, a church, serf's homes, a pasture, a water mill, fields, and a barn.
Monarchs (kings and queens) had absolute power. They provided land to others. They received their power because they maintained control of their kingdoms before becoming a monarch and some had enough wealth to afford their own armies. They also believed that God made said that they should rule.
A lord/noble was an extremely wealthy land owner, but not as rich as a monarch. Nobles/lords usually owned the manors. They provided land for the others living in the manor.
Vassals were also rich people but they instead provided horses, shelter, weapons, food and clothing for the knights.
Knights were medieval soldiers who protected the people living in the manors. They provided protection and they were loyal to everyone in the manor. Three stages of becoming a knight included page, which was being a servant for a noble at the age of seven, and then when they the knight in training became a teen, they'd become a squire which was taking care of their armor and horses and such, and being introduced to hunting as well. Then, they'd become a knight.
Serfs were poor people and borderline slaves, except they could leave. But if they left, they'd have nowhere to go. They provided food and services to the people living in the manor.