Okay kiddo, let me tell you about simple lie groups! Imagine you are playing with legos, and you build a big structure using different kinds of lego blocks. Now, imagine that you want to describe how two people can move the structure around while keeping it the same shape. That's what a lie group does -- it helps us understand how things can be transformed while staying the same.
A simple lie group is a special kind of lie group. It's like a lego structure made from very simple blocks that can't be broken down into smaller blocks. Think of these simple blocks like the basic building blocks of a language -- you can't break them down into even smaller parts. In the same way, you can't break down the basic blocks of a simple lie group into anything simpler.
Simple lie groups are really important in math and physics because they help us understand the symmetry of certain shapes and equations. It's like if you have a simple lego structure, you can easily see how it can be transformed and changed. Simple lie groups help us do the same thing with more complicated shapes and equations.
So, in summary, a simple lie group is like a lego structure made from simple building blocks that can't be broken down any further. Math and physics experts use them to understand how things can be transformed while staying the same shape.