There are festivals and times of celebration that pagans/wiccans generally celebrate. These can be found on the "wheel of the year" if you google. Interestingly enough, most of these days fall on or near christian holidays. That is because the christian leaders believed it was easier to convert the peasants if they kept the same days and just renamed them.
Excellent articles are written by Starhawk who is a activist witch
Her books are good, too. Not all books offer great advice, though. It is part of the learning process to read and learn as much as you can so you can tell who the good ones are.
Scott Cunningham wrote a book titled Wicca: A Guide for the Solitary Practitioner which is wonderful for those starting out.
There isn't any need to have a formal coven or guidance person. It may make it easier to have a community around, but it isn't needed. We all are born with what we need inside of us. Whatever feels right and natural is what is perfect for us. Many people appreciate the company while others see spirituality as something more personal.
The past few years while I was in school, I had a teacher who was a witch and had a doctorate in Theology. She was fascinated by rituals practiced by all peolple and religions. Her classes were always full. She comes across as the absent minded professor at times, but her knowledge base is extensive.
Something else that is a bit confusing; are all wiccans pagan and vice versa? Pagan is an umbrella term. Wicca is a more narrowed down version. There are many belief systems that fall under the pagan title - druidism, Celtic, Slavic and many others.
One does not just simply buy a book and "become" wiccan. It is a process as another member posted. A year and a day is the recommended time to explore and learn about what is real for you and what works for you. There should be no pressure from anyone that you hurry up and "become a witch". It takes time to learn of the traditions and systems. Even wiccans are different in what they believe - there are tradional, Gardnerian, reconstructionist, and so on.
Just like with all things involving humans, some people are drawn to paganism or wicca for the wrong reasons. It could be to be popular, to be different, to make their parents angry, to try to harm others with bad magick.
To me, black magic is simply intently wishing harm upon another. I am not convinced of its power. White magick is (as another member said) prayer with intent. It is a prayer that is focused and guided. It is my belief that good will ultimately win.
There are also many ways to conduct a ceremony. They can be long, large and lavish or they can be simple, direct and beautiful. The four directions are often called upon. The four directions are ancient and show up in many cultures and belief systems. They represent the four elements: water, earth, fire and air.
I hope this has helped some. I didn't realize I would ramble on in book-length!
edit: reading the articles on witchvox.com will help explain a lot