Wicca is a duotheistic religion. That is, Wiccans worship two separate and distinct Divinities: the Goddess and the God. Unlike some other duotheistic religions, such as Zoroastrianism, where the two Divinities are adversaries, locked in an eternal struggle between light and darkness, or between good and evil; in the Wiccan belief system the God and the Goddess are partners, each being the others complement. In the Wiccan creation myth, the universe in which we find ourselves is seen as being the child of the God and the Goddess, engendered when the God and the Goddess come together in what is called the Sacred Marriage.
Wicca is commonly called a nature religion, or a nature-oriented religion. Both of these are misnomers: Wicca is, at its heart, a fertility religion. Wiccas central creation myth is wrapped around the coupling of the Goddess with the God in order to bring the Universe into being, and all Wiccan observances include either a symbolic or an explicit re-enactment of that coupling by the officiating priest and priestess as the central ritual element that sanctifies and hallows the entire undertaking. The energies that empower Wiccan rituals are therefore, at their roots, sexual energies; and Wicca is one of the few religions in which coitus can be seen a sacramental act.
This is not to say that Wiccans are cavalier about their relationship with the natural world. Wicca is a panentheist religion, seeing the Goddess and the God as being both transcendent and immanent at the same time. Because the Universe is, in the Wiccan scheme of things, the child of the God and the Goddess, some portion of both the God and the Goddess is present in every thing that exists. By that token, all that exists is therefore due a portion of the respect, honor, and worship that Wiccans offer to their God and Goddess. At the same time, the natural processes inherent in the Universe, the processes of birth, growth, life, death, and decay (which eventually leads to new birth and growth,) are equally part of Creation and entitled to the same consideration. The premise that all that is is in some part Divine explains why many observant Wiccans argue that Wiccans should structure their lives so as to fit easily into the natural world as opposed to forcing the natural word to conform to whatever ideas they may have that seem most convenient at the time.
At the same time however, Wiccans also see their Goddess and God as being transcendent, as being entities existing separately and apart from the Universe, yet able still to reach back into the Universe and alter its nature as They may see fit. It is this transcendent nature attributed to the Goddess and Her Consort that requires that Their Presence be invoked as part of Wiccan ritual, since without such a specific invocation, the Divine Presence inherent in the natural world is at best incomplete and imperfect. After all, howsoever much a child may resemble its parents, the child is not the parent.
Wicca is also a magical religion, holding as an article of faith the idea that the Goddess and the God have given unto their children the same ability to alter the fabric of the Universe that they themselves possess, and that this ability is gained by means of the energies raised by the ritual re-enactment of the Sacred Marriage. The phrase commonly used to explain this is As above, so below. By this it is meant that as Wiccans mirror the actions of the God and the Goddess, so too are the results of the Sacred Marriage mirrored in the natural world, giving Wiccans access to the same energies by which the world was made, that they might alter the world into a form more to their liking.