Okay, so imagine you are standing still in the middle of a room. If you turn to the left or right, you can see everything in the room from a different perspective. This is kind of like the Lorentz group, which is a fancy name for a group of mathematical transformations that tell us how to change our perspective when we look at objects moving really fast in different directions.
Now, think of your body as an object that can move and rotate around in the room. Your arms can go up and down, your head can tilt, and your legs can stretch out. This is kind of like what we call a "representation" of your body in different positions and orientations.
Similarly, in the Lorentz group, we have different "representations" that describe how objects move and rotate in different directions and at different speeds. These representations are like different ways of looking at the same object, just like how you can see everything in the room from different angles.
Scientists use this representation theory of the Lorentz group to better understand how particles and waves behave when they move at very, very fast speeds like in the universe or in particle physics experiments. They also use it to study things like quantum mechanics and relativity, which are both really important ideas in physics.
In short, the representation theory of the Lorentz group is like a set of rules that helps scientists better understand how everything moves and behaves in the universe, kind of like a big instruction manual for how to make sense of everything around us.