Wicca is an Earth-based religion the falls under the broad category of "Pagan". The people who follow Wicca are known as Wiccans. Those Wiccans who chose to practice magic (or magick) with their faith can be known as "Witches" or Wiccan Witches". The word "witch" also covers the male population. Wicca followers are not only women, but there are male followers as well.
Wiccans believe in one central Divine force that come into the two main forms of a Goddess and a God. They are both regarded as equal, although some feel more drawn to one than to the other. Wiccans also have the freedom of working with or worshipping many other deities if they please.
Wiccans, as well as other Pagans, celebrate holidays that go along with the Earth such as the Summer and Winter Soltice and the Spring and Fall Equinox. Some also have small celebrations on full moons. When the church was trying to spread Christianity, they made most of their holidays near Pagan holidays so the people would feel more comfortable switching religions. (In fact, most scholars agree that Jesus was not born on December 25th. They just use that day to celebrate his birth becasue it was an old Pagan holiday called Saturnalia or Yule.)
If you trace back many symbols of Christmas for instance, such as the mistletoe, evergreen tree, wreath, colors of red and green, most of them have pagan roots.
Although there is a lot of freedom in Wicca to worship and believe what you please, there are still two "laws" or "guidelines" that they follow and believe. The first one is called the Wiccan Rede and in simple terms states that you can do whatever you want as long as it brings no harm to yourself or others. The other law that they follow and believe in is the Law of Karma. (whatever goes around comes around sorta thing.) The Law of Karma says that whatever energies you put out into the universe, whether negative or postive, will come back to you 3 fold.
Wicca is an interesting religion that no one has to be scared of if they take the time out to learn.