Imagine you have a toy that you love playing with but one day accidentally drop it on the ground. Once you pick it up, you notice there's a big crack on it and it doesn't work like it used to. That's damage!
In the same way, when something in the real world gets damaged, it means it's not working as well as it did before. For example, a car that has been in a crash may have a broken bumper or a flat tire, which can make it hard to drive.
Damage mechanics is a way of trying to understand how things get damaged, how bad the damage is, and how to fix it. Just like a doctor will look at your body and determine what's wrong and what medicine or treatment will help you feel better, damage mechanics experts use science to figure out how to fix things that are broken.
They might study how different materials like metal or plastic respond to being hit, bent, or twisted. They could also try to find out how much pressure something can handle before it breaks or how different liquids or chemicals affect materials.
Basically, damage mechanics is like being a detective and trying to figure out what happened to the toy to make it break, so you can prevent it from happening again or fix it.