Imagine you have a big toy box with lots of different toys inside. Now, imagine you have a special rule about how you're allowed to take toys out of the box and play with them. Let's say that whenever you take a toy out to play with, you have to put it back in the exact same spot you got it from. You're not allowed to move any of the other toys around or change the way the box looks inside.
This is kind of like what a measure-preserving dynamical system is. It's a way of studying how things change over time, but with a really strict rule about what you're allowed to do. In this case, the "toys" are points, and the box is a "space" where those points live.
The idea behind a measure-preserving dynamical system is to look at how points move around in this space over time, but without changing any of the important features of the space. These might include things like its shape or size, or how densely packed the points are in different areas.
To make this work, mathematicians use a bunch of fancy techniques to carefully track the movement of each point in the system. They also make use of something called a "measure", which is a way of assigning a number to different parts of the space. This measure tells you things like how big a certain area is, or how dense the points are in that region.
By keeping track of this measure over time, mathematicians can study how the points move around without changing any of the important features of the space. They can also use this information to make predictions about what will happen in the future, and to understand how different parts of the system are related to each other.
So, in summary, a measure-preserving dynamical system is kind of like a toy box with a bunch of rules about how you're allowed to play with the toys inside. It's a way of studying how points move around in a space over time, without changing any of the important features of that space. And by carefully tracking this movement, mathematicians can learn a lot about how the system behaves and how different parts of it are connected.