Explained variation is like when you are making a picture and you use different colors to make it look pretty. The colors you use are the things that explain or show why your picture looks like it does. This is what we call "explained variation."
Let's say you are drawing a picture of a tree, and you use brown and green colors for the trunk and leaves. This helps explain why the picture looks like a tree. The colors you used are the "explained variation" in your picture.
It's kinda like when you see a cookie on a plate, and your mom tells you that she used chocolate chips to make the cookie taste good. The chocolate chips are what explained why the cookie tasted good. They helped make the cookie yummy!
Explained variation is important because it shows us why things happen or look a certain way. In school, your teacher might ask you to explain why a math problem turned out a certain way. The numbers you used to solve the problem are the "explained variation" that show why you got the answer you did.
So, explained variation is really just a fancy way of saying we can understand why something happens or is the way it is by looking at the things that explain it.