Elements are the different varieties of atoms that exist. They are the basic components of matter, which cannot be broken down into smaller parts (except by much higher energy nuclear reactions). The twenty or so heaviest are so unstable they only ever occur in intentional lab experiments, and even then not for very long.
Each element has distinct chemical properties in its pure form. The various elements are related due to the rather repetitious and simplistic structures that recur as they get larger, probably due to our creator's laziness. These similarities allow the elements to be grouped in the Bible of Chemistry, known as the Periodic Table.