Earth is the element most closely associated with manifesting. Manifesting could also be called creating, or fulfilling your goals. When you want something in your life, whether it is a material thing such as a house or a new iPod, or perhaps a love relationship, or your Master's degree, or something more abstract such as inner peace or mindfulness, you work toward bringing what you desire into your experience. You do that by bringing your thoughts and feelings into harmony with what you want.
Sometimes the work of manifesting is slow and deliberate. You might do a bunch of research, choose a college, save money for tuition, apply for a Master's degree program, and look for financial aid. Only then do you sign up for classes and purchase books...and that's just the beginning. You still have two or three years of academic work before the sought-after degree is yours. The element of Earth is the foundation of the physical-realm work that you are doing. Earth sustains you over the long haul, helping you see the ultimate goal that you've set out to attain.
Other times we seem to manifest our desires almost overnight. After I lost my Subaru in an accident a couple of years ago, I visualized the replacement car I wanted. The check from the insurance company arrived promptly, I did a very short search, and then found the exact car I had pictured, with all the features I wanted. It seemed like I didn't need to put that much work into manifesting the new vehicle (granted, that same car's engine decided to quit less than a year after I got it, but that's another story...or perhaps a lesson for me about trusting my creations).
Either way, slowly or quickly, we are using the energies of our mind, body and spirit to influence what happens to us. Whether we do this consciously and intentionally or not is up to us. Having goals and aspirations is helpful, as it gives us something to work toward. Yet we also need to avoid clinging too strongly to particular outcomes, because that can keep us from moving forward. If we get too invested in what we wish to manifest, we can get stuck, which is part of the shadow side of Earth energy.
Ultimately, matter is still energy, at its root. Everything is moving, even huge boulders that appear to have been sleeping in the same place for eons. Protons and electrons are in constant motion, and the space between them leaves plenty of room for mystery. Our own moving energies affect what shows up in our lives, and by working in concert with the Earth element, we can achieve our heart's desires.