Okay kiddo, so the Academy of Criminal Justice Sciences is like a really big club for people who study things like crime, the law, and justice. This club helps these people learn even more about these things by providing them with resources and opportunities to share their ideas with others who are interested in the same things.
Think of it like a big playground where everyone who likes playing detective or learning about laws and how to make them better can play together and help each other learn new things. The grown-ups in charge of the playground, or the Academy, make sure everything is fair and everyone gets a chance to play and learn.