Elements are atoms that have a certain amount of protons. The number of protons an element has is its atomic number.
Example:
All atoms that have 8 protons are the oxygen element.
Each element is given their own chemical symbol. The chemical symbols of elements are usually an abbreviation of the elements name in english. The chemical symbol for the element oxygen is O.
The atomic mass of an element can vary, though the atomic number of each element cannot change. When different atoms of an element have different atomic mass numbers, they are known as isotopes.