These are the five elements of creation. It is their interaction that creates Mana, the energy of magic. Perhaps the best known treatise on the interaction of the 5 elements to produce Mana is that by Heward.
Each of the five elements exists in their raw form in their own dimension, or plane of existence. It is the intersection of the five elemental planes that forms the Planes of Man. The entire physical world is nothing but a collection of objects constructed from these five elements.
The first four are generally familiar to most individuals as the encounter reflections of these elements within their every day life: the dirt beneath ones feet, the air one breathes, the fire one cooks dinner with and the water one must drink to live. The fifth however is less well known, and while it is omnipresent it is also elusive and ephemeral.
The fifth element, spirit sometimes referred to as Animae or the Element of Man is the raw essence of the life force. That which we call life is matter from the combination of the first four elements, infused with spirit or animus. Animus is the reflection of Animae on the Planes of Man.
All of nature is dictated by the interaction of the elements, Astrology is the science that tells us how.