Okay kiddo, constabulary is a big grown-up word that refers to a group of people who are in charge of making sure that everyone follows the rules in a certain area.
Think of it like your teacher keeping an eye on your classroom to make sure you and your classmates are following the rules, but on a much larger scale.
These constables or police officers have a special job which is to make sure people behave well and do not break the law. They help to keep us safe and make sure our community is a happy place to live in.
So basically, the constabulary are a bunch of people who help make sure everyone follows the rules and stay safe in their town or city. Does that make sense, kiddo?