Okay kiddo, let me explain about Judges chapter 9 in a way that you can understand.
There was a guy named Abimelech. He was the son of a judge named Gideon who used to rule over Israel. After Gideon died, Abimelech wanted to rule over Israel too, but the people didn't want him to be their leader because he was not a good person.
So Abimelech and his army attacked the city of Shechem and took control of it. Then he made his way to another city, Thebez, but the people there didn't want him to be their leader either. They went to a tower and locked themselves inside to hide from him.
Abimelech got really angry and ordered his soldiers to burn down the tower with the people inside. But as he was standing near the tower, a woman threw a millstone from the top of the tower and hit him on the head. Abimelech was badly hurt but not dead, so he asked his armor-bearer to kill him so that people couldn't say he was killed by a woman.
The story ends by saying that God punished Abimelech for his evil actions and the people of Israel went back to following God's laws.
So, in short, Judges 9 is a story about a bad guy named Abimelech who tried to become the leader of Israel but was not successful and met a bad end.