Smoking is when you use a small stick called a cigarette that has leaves inside it. When you light it up, it produces smoke that you breathe in. This smoke is not good for your health and can make you very sick over time. That's why a lot of people don't want to be around smoke.
When people drive in their cars, they are in a small space that can fill up quickly with smoke from cigarettes. This is why some places have made it illegal to smoke in cars. It's like when your parents tell you to open a window if you let out a stinky fart - they want to get rid of the bad smell.
So, some people have decided that it's not safe or healthy to smoke in cars, especially if there are other people in the car with you. And if you get caught smoking in your car where it's not allowed, then you can get in big trouble and might have to pay a lot of money. So it's better to just not smoke in your car and keep yourself and others safe!