An affiliated school is like a special kind of school that is related to a bigger or more important school. Think of it like having a big brother or big sister. The bigger or more important school is the big brother or big sister and the affiliated school is like the little brother or little sister.
Sometimes big brother or big sister will help out little brother or little sister by giving them some of their supplies or letting them borrow things. That's kind of like what an affiliated school is. The bigger or more important school has some things that the affiliated school can use or they might help with special programs or activities.
So, in short, an affiliated school is just like a little brother or little sister school that gets help from a bigger or more important school.