Castles: A Nobles power depended on his ability to defend his land. Walls were good, Castles were better. The first castles were made of mud and wood. But wood burns so around 1100 CE people switched to building them out of stone. With thick stone walls surrounding the manor house and village the people felt safe. Most peasants did not live in the castle, but when trouble came they would hurry inside the castle and close the gates.
Location: Castles were built to be the highest point around so if there was a hill the castle went on top. This meant you could see trouble a long way off. You could also throw things down at any attacker. Some castles were surrounded by a moat which was a deep ditch filled with water. A small bridge was built to lower and raise as needed over the moat. This was the drawbridge.
Interior: The interior of a castle contained The Keep, a storage space for food in case of siege, also the last line of defense in the Castle; Barracks which were the homes of the Knights and soldiers of the Noble; The Great Hall, a place to feast and meet the noble during formal occasions; The Chapel, a place to hold religious services and Gatehouses which were secure places that guarded the gates.