Don't worry, this video isn't about all about math. Rather, it aims to give you an intuitive understanding of one of the most fundamental laws of physics related to photography and shows you why it's so crucial to have a solid understanding of how it works.
If you read a bit about cognitive psychology, you'll see that humans are really terrible at estimating non-linear phenomena, which is why stuff like the way light intensity changes with distance can throw us for a loop, particularly when we're first starting in photography. This helpful video from Joe Edelman will explain (in more practical, non-mathematical terms) how the inverse sqaure law works, what consequences it has on lighting for photographers, and what principles to keep in mind when you're shooting so you can get the shot you desire. While you can dive into modifiers and CRI and all sorts of things all day when it comes to lighting, if there's one principle that will have the greatest effect on your output, this is it; so, make sure you really know it as well as possible.
Just a note, at 4:00, Edelman says at quadruple the original distance, the light intensity is 1/6th the original amount; it's actually 1/16th. Otherwise, the information is all quite sound and helpful!