Have you ever played with toy cars and then smashed them together? When two real cars crash into each other, people called accident reconstructionists try to figure out what happened and why to help prevent it from happening again.
They look at things like skid marks on the road, the damage to the cars, and the speeds they were going to "reconstruct" the accident like a puzzle. They might use special tools like lasers to measure distances and angles, or take pictures and videos to help them better understand what happened.
Sometimes they even build a mini model of the crash scene to test out their ideas and see if they match what actually happened. By understanding how accidents happen, they can make our roads safer and prevent more crashes from happening in the future.