A siege is when the enemy would surround the castle. No-one could go in or out. When the people starved to death, the enemy would attack them and take their castle.
The siege tower was made out of wood and bricks. In the side of the tower were ladders to the top so you could shoot your arrows in the castle. Also in the front view, there was a door that swings down and becomes a ramp. They would use ladders but the other people were smart and they would push you off the ladder or they would put hot boiling water or hot oil down the ladder. If the enemy made it up, they would destroy the people in the castle.