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Everything is made up of matter. The simplest forms of matter are elements. An example of an element: Hydrogen (H), Oxygen (O) and Gold (Au). When elements are broken, molecules are their smaller parts. When two or more different elements combine, they create a compound. An example is: Water (H2O) - [2 Hydrogen Atoms + 1 Oxygen Atom], Salt (NaCl) - [1 Sodium Atom + 1 Chlorine Atom].

Here is an example of a molecule and a compound:

The two H atoms produce a H molecule. On the right, the H molecule combined with one O atom will produce one Water molecule of the compound H2O.

Braking down an atom, will give you some atomic particles. These particles are electrons (negative charge) and protons (positive charge). There is a nucleus in an atom, comprising of neutrons (no charge) and protons. The nucleus is most of an atom's mass.

Atoms have shells, the rings on which electrons orbit the nucleus. The more electrons, protons and neutrons an atom will have, the more shells it will have. Take a look: