Wicca 101
These days alternative religions are so popular that people are introduced to witchcraft and Wicca in all sorts of ways. Often their next step is to visit a bookstore, where they search for the best beginner witchcraft books. These books are sometimes referred to in the pagan community as "Wicca 101" books, since they generally contain a lot of the same material, on subject that new practitioners need to pick up quickly.
What You Can Learn From Beginner Witchcraft Books
The topics covered in Wicca 101 type books generally include a short history of witchcraft or Wicca, an overview of the beliefs of modern witches, information on basic spellcasting, the holidays celebrated by witches, and so on. The differences between the books are mostly in the details, and may also depend a lot on the author's personal beliefs and writing style. In many cases one beginner witchcraft book is pretty much as good as another, but you want to make sure you find one that speaks to you in a language you enjoy.
Witchcraft Vs. Wicca
Something that casually interested readers may not realize immediately is that there are significant but complicated differences between the concepts of witchcraft and Wicca. Witchcraft is an ancient magical tradition. Usually the word refers to the shamanic practices native to Europe, although similar concepts exist in many parts of the world. Witches often follow a pagan religion (although there are definitely exceptions, including atheist and self-identified Christian witches). Wicca is a pagan religion that was founded in the early 1900s based on ancient pagan traditions and ritual magic, but incorporating a specific set of beliefs and rituals. To further confuse matters, the words "wicca" and "witch" probably come from the same root (meaning "wise"), and many Wiccans refer to themselves as witches (although non-Wiccan witches pretty much never do the opposite). Be aware of this distinction when choosing beginner witchcraft books, and try to choose a book that actually has "Wicca" in the title if that's what you're looking for.
My Beginner Witchcraft Book Picks
After a thorough review of a lot of beginner witchcraft books, here are a few I can recommend.
The Spiral Dance, by Starhawk, is a real classic that clearly lays out the basics of modern witchcraft. It's an especially good pick if you're interested in ecology or feminism, since Starhawk definitely believes that religion and politics should mix. She also approaches magic from a somewhat psychological perspective, which can be nice if you're a bit skeptical (or potentially offputting if you like your magic a little more, well, magical). Starhawk is a major thinker in paganism today, and she has also written several related books on more advanced topics.
Embracing the Moon, by Yasmine Galenorn, is another excellent choice. If I had to pick just one beginner witchcraft book, it would probably be this one. Galenorn goes over the basics solidly and doesn't shy away from "dark" topics, but the book really shines when it comes to spells and rituals. Finding good poetry in pagan books can be tough, but in my opinion this book is an exception. One drawback is that she barely discusses the common pagan holidays. This information is easy enough to find elsewhere, but it's a slightly odd oversight.
A Witch Alone: Thirteen Moons to Master Natural Magic, by Marian Green, is a good choice if you're looking for an accessible book that you won't outgrow too quickly. This book is designed as a one year course, and it's a serious commitment involving a lot of personal work and contact with nature. It's probably most appropriate beginner witchcraft book if you're hoping for a quick read, aren't deeply motivated to work through the exercises, or live in an urban environment.
The Temple of Witchcraft Series, by Christopher Penczak, is a new one, but it looks promising. The series currently includes four books, on the topics of magic and meditation, circles and rituals, shamanic practices and healing, and an introduction to ritual magic. I like the organization of this series, and believe that this expanded set of topics would be extremely useful to beginning witches. Penczak is currently working on a more advanced series, too, so fans of his work have plenty to look forward to.