Canon law is like a big book of rules and guidelines for people who follow the teachings of the Catholic Church. Just like how your parents might have rules for you to follow at home, the church has rules for their members too.
These rules cover things like how to get married in the church, how to become a priest or nun, and how to behave during religious services. They also include rules on how to handle things like disputes and disagreements between church members or what to do if someone breaks one of the rules.
The people who make up the rules are called canon lawyers, and they use the teachings of the Church, along with other important documents and laws, to decide what should be included in the canon law. It's like a big guidebook that helps everyone who follows the Church know what they should be doing and how they should be doing it.
So just like how you have rules to follow at home, the Church has rules to follow too, and they are all included in the canon law.