Magic is manipulating the powers of nature (energies) to achieve needed results. It is connecting with the energy that is present in our everyday world, and directing it where we need it to go. As part of the religion, most Wiccans practice magic as a way to purify physical space and work good deeds.
Magic isn't really much different than some of the Judeo-Christian concepts for prayer... except Wiccans understand that we have the ability to make the changes -- not just some omniscient deity. By working through the Goddess and the God (in whatever form they take), we are able to sense and direct the energy of nature and use it to bring about changes. How effectively a Wiccan can work a spell depends on many factors. Being able to tap into the natural rhythm of the world to sense and direct the energy is the biggest factor. By connecting with the Goddess and the God, Wiccans are able to cast magic spells to make the world we live in a better place.
Now you're probably thinking, "Yeah right -- what magic energy?" Just because you can't see or feel it, doesn't mean that it doesn't exist. Can you see the electromagnetic waves that carry your TV or radio signal? No -- but we've built special receivers that can. So why is it so hard to believe (or more correctly, understand) that there can be other forms of natural energy that we don't normally see or feel? By connecting with the God and Goddess, we are able to build our own "receivers" that allow us to sense and direct the energy that exists around us.
