Okay, think of a car like a big toy truck. You know how sometimes you need to put batteries in your toy truck to make it go? Well, a car needs something called fuel to make it go.
But sometimes, the fuel that we put in the car isn't very good. It might be dirty or not have enough good stuff in it to help the car run smoothly.
That's where a fuel additive comes in! It's like a special toy truck battery that we add to the fuel. The fuel additive helps make the fuel better so that the car runs better too.
It can help clean out any yucky stuff that might be in the fuel, and it can add more good stuff to help the car's engine work better.
So, think of the fuel additive like a magic potion that helps the car be the best it can be!