Active fuel management is like having two kinds of fuel in your car. One kind is used when you need to go fast or drive up a hill. The other fuel is used when you don't need to go as fast or drive on flat roads.
Just like when you have a lot of work to do and you need to focus, your brain uses a lot of energy. But when you're just relaxing, your brain doesn't need as much energy. Active fuel management works the same way - when your car needs a lot of power to accelerate or drive up a hill, it uses one type of fuel. When the car doesn't need as much power, it switches to the other type of fuel to save energy.
This helps your car be more efficient and use less gas, which is better for the environment and your wallet!