This is what a siege looked like.
A siege of a castle is where a group of knights set up campsites outside of a castle and didn't let anyone out of the castle. So the castle will run out of food and water and that is when the knights outside of the castle attack, because the castle is weak and the people in the castle have no food or water . Some time a sieg can last for months and even a year until the castle runs out of food. The meaning of doing a siege is to weaken your enemy by making them lose water and food and none of your knights get hurt.
A trebuchet is a weapon that knights used to knock down walls of a castle. A trebuchet is kind of like a catapult . The trebuchet throws rocks and sometimes dead bodies that had the plague across the castle walls. So the knights defending would get the disease. To work a trebuchet, you pull a lever and then tie the rope attached to the lever to something. To launch the trebuchet you cut the rope.