Okay kiddo, so peroxynitrate is a molecule that is made up of two different things - nitrate and peroxide. Nitrate is a substance that is found in things like fertilizer and explosives, while peroxide is the same stuff that you put on cuts and scrapes to make them feel better.
When nitrate and peroxide combine to make peroxynitrate, it becomes a very reactive substance that can damage parts of our body like our cells and DNA. It's kind of like when you mix vinegar and baking soda together and it fizzes up and makes a mess - peroxynitrate does something similar inside our bodies.
Sometimes our bodies make peroxynitrate as part of our immune system, to help fight off infections. But too much peroxynitrate can cause problems, like inflammation and damage to our tissues.
That's why it's important to try to stay healthy and avoid things that can cause our bodies to make too much peroxynitrate, like smoking and exposure to pollution. And if we do have too much peroxynitrate in our bodies, there are medicines and treatments that can help to get rid of it and keep us feeling well.