Okay, kiddo, imagine you want to color in a big picture of a park. You have lots of different colored crayons and you want to use them all in different parts of the picture. But you don't want to color way outside the lines and make a mess!
An area source is kind of like a coloring book page. It's a specific area where something is happening that might produce pollutants or things that can harm the environment. That area can be a factory, a farm, a big parking lot, or any other place where lots of people and things are concentrated.
Just like coloring inside the lines, people and businesses in these areas have rules they have to follow to make sure they're not polluting too much. These rules might make them use special equipment, change the way they do things, or even limit how much of a certain substance they can use or produce.
The rules are important because they help keep the environment clean and protect the air we breathe and the water we drink. Like how you don't want to color outside the lines and make a mess, we don't want these businesses and activities to harm our environment and make a mess.