A Wiccan is a follower of a Nature-Based Mystery Religion that honors a Goddess as well as a God and lives in accordance with the Wiccan code of Ethics.
So let's tackle this in pieces: what is a Nature-Based Religion? In ancient times people lived much closer to the land. their lives were more closely tied to the ebb and flow of the world around them: the seasons, the tides, sunrise, sunset. In the Spring they planned, planted and prepared. During Summer they were busy harvesting crops and life was full of action. In the Autumn they tended to the things that they were forced to put aside during the busy season and prepared for the long winter ahead. Winter was a time of reflection.
Ancient people drew parallels between the Wheel of the Year, their lives and their days. They discovered that by living in harmony with the ebbs and flows of the Nature their lives became both easier and happier. As modern Pagans we also try to live in harmony with the world around us but our world now includes technology, cities and all the marvels of modern society. But Nature does not end at our doorstep and understanding the world we live and living in harmony with it can still greatly enrich our lives.
Wicca is also a Mystery Religion. This means that we believe some lessons can not be read from a book, they must be experienced to understand. For instance one of the mysteries of the Goddess is that she is three in one: she is the Maiden, the Mother and the Crone. Three different faces and yet she is the same Goddess at all times. In the same way you are a different person at work, with your family, your spouse, your closest friends... and yet you are still just one person. I can tell you this but you won't truly understand the ramifications of this simple statement until you experience it for yourself.
Tying these ideas together (Mystery and Nature-Based Religion) we find that Nature is our classroom, you may be playing with a pet, working on tricky puzzles, gazing at raindrops falling into puddles... and suddenly you will just “get it”. Our lessons come from everywhere and so our Religion has nothing to fear from Science, Progress or Truth for these things can only add to our understanding of our Religion.
In Wicca we use tools such as the Meditation and “The Charge of the Goddess” to create an environment within which you can experience and learn these mysteries. We also incorporate many balances into our Rituals to help us get into a proper frame of mind and explore the world around us for Mysteries. Some of these balances include the Pentagram which includes a balance between the classical elements (Earth, Air, Fire, Water and the fifth - Spirit), The Triskelle (Land, Sea and Sky as seen when casting a circle three times round), The duality of Masculine and Feminine energies and the Wheel of the Year.
The other thing that defines Wicca is our code of ethics. This can be summed up in the Threefold-Law (that which we do affects us Mind, Body and Soul) and the Wiccan Rede (Harm None). An entire class will be devoted to these two since they hide a lot in their simplicity.
This is Wicca. Wicca is an active, learning path where a lot of the work will be on you sine we are each potentially our own High Priests and High Priestesses. We make up our own minds about what feels right, but we are also the ones that we must turn to when we need spiritual guidance for knowledge must come from within before it can come from without. We all have the same tools and should respect each other, and where we find commonality is where we will find the Truth.