The Elements, Earth, Air, Fire, and Water, create everything. You could call them the first phases of manifestation. The Qaballah tells us that the Elements were created in the following order, Air, Fire, Water, and Earth, each becoming more and more corporeal, and dense.
The Elements can be used powerfully in ritual. Of course, to use them in ritual, you must know what they correspond to (hence the term "correspondences"). Below is a short list, which is by no means definitive, but hopefully it'll help you out a little. For simple things (which is mostly what is done anyhow), the Elements and a few other symbols suffice. Of course, the more correspondences you add, the better off you will be.
Associated With | Money, Wealth, Soil, Plants, Growth, and all material and mundane matters. Can also be associated with death and dying, decay. |
Direction | North |
Archangel | Auriel |
Color | Green or sometimes black |
Tarot Suit | Pentacles |
Magickal Weapon | Pentacle, or salt |
Elemental | Gnome |
Qualities | Dry and Cold |
There will, of course, be more to come, but I seem to be lacking some of my books for some reason. I'll have to find them. Of course, there are already some books which have a marvelous amount of correspondences, not just for the elements, but for all of them. In particular, Liber 777 by Aleister Crowley is an excellent source. And, if you don't have or want to buy this book, then there are sure to be some sites under my Links section that will have the information you want.