The stuff of which the universe is composed, has two characteristics: it has mass and it occupies space. Matter comes in a great variety of forms: the stars, the air that you are breathing, the gasoline that you put in your car, the chair on which you are sitting, the turkey in the sandwich you may have eaten for lunch, the tissues in your brain that allow you to read and understand this sentence, and so on.
As we lokk around our world, we are impressed by the great diversity of matter. Given the many forms and types of matter, it seems difficult to believe that all matter is composed of a small number of fundamental particles. It is surprising that the fundamental building blocks in chocolate cake are very similar to the components of air.