Okay kiddo, have you ever seen a train before? Good! A train is made up of a lot of train cars that are connected together. Each car has a different job, some are for carrying people, some are for carrying cargo.
Now imagine all the train cars are the same size and can only carry one thing. That means if you have a big thing that won't fit in one car, you have to split it up into smaller pieces that can fit.
The boxcar function works kind of like this. It takes a big thing, like a signal or a sound wave, and breaks it up into smaller pieces. These smaller pieces are called "boxes" and they are all the same size.
Why do we need to do this? Well, sometimes we need to analyze signals or sound waves and it's easier to do that if we break them up into smaller parts. We can look at each box and see how much of the signal is in that box.
So think of the boxcar function like a train taking a big thing and breaking it up into smaller pieces so we can better understand it. Pretty cool, huh?