Everything is made of something. Nothing is made of nothing.
Chemistry is about the smallest things that other bigger things are made of, and what happens when they change. The word chemistry comes from chemical, which is an example of one type of the very small things that other bigger things are made of. The words you are reading now are made of a dark liquid called ink (墨水), which is written on paper. The paper itself is made out of the chemicals that wood is made out of. Both the ink and the paper were made by different chemical processes. A chemical process is what happens when chemicals come together to make other chemicals, and therefore other things.
Cooking makes chemical changes. Your different ingredients are made of different chemicals, and when you put them together and make them hot and cook them, the chemicals change into new chemicals and the different ingredients make something new. That tomato sauce you're making is made of tomatoes, onions, garlic, salt and pepper. Those ingredients each have their own chemicals and their own flavors, but now with your sauce you've made something different, something that has its own flavor, all the ingredients mixed together, all the chemicals mixed together, something new.
You can smell the chemical changes, too, as they go up into your nose, especially when you forget about your sauce and it doesn't just cook but bums and becomes black and has a really bad flavor. You can't make it better, either, because once chemicals change, they can't be changed back again.
