As vast as the universe is, everything in it consists of very small parts assembled in particular ways.

What is Matter?

Everything in the universe is made up of either stuff or empty space. The "stuff" in the universe is called "matter". The empty space is called... space. Remember that matter encompasses not just solids and liquids, but also gasses like the air we breathe. In space there is no liquid or gas; there is no matter at all.

Molecules

The primary fundamental part of most things that you encounter day to day is called the molecule. A molecule is the smallest part of a thing that still exhibits the same fundamental properties of that thing. If you take some substance and keep breaking it into smaller and smaller pieces, stopping only when breaking it into a smaller piece would change what it is, then you have a molecule.

Elements

Molecules consist of entirely one element.

Getting any smaller than a molecule, you'll be talking about particles of matter that don't ordinarily exist in a way that you can use them. There are only a handful of molecules