Witches and Wiccans usually keep a "Book of Shadows", which can be a confusing item for anyone just learning about witchcraft. Most people misunderstand it, and think that there is *a* Book of Shadows, as one single book that witches use for spells. Some ancient grimoire passed down for hundreds of years, and the only real source for true magick.
Makes a good TV series, but that's not how it works. A Book of Shadows is a personal book of spells that you write for yourself. Different people have different books, usually referred to as a BoS. Technically, another term would be "grimoire" but people don't really use that in general conversation. Some witches prefer to call theirs a Book of Light, or any number of other terms. It's not set in concrete, but the most common term for a witch's book is a Book of Shadows.
What to Write In
Most people would love to have a leather-bound book, bound with parchment paper pages. Some nice metal embellishments and even a buckled strap around it would be quite nice. There are books out there like that so that is definitely an option. Since most witches are creating the BoS over many years of witchcraft practice, it's more helpful to have a book that allows for pages to be removed or inserted rather than a sold bound book.
For a really practical Book of Shadows, most experienced witches will recommend a 3-ring binder. No, it's not the most mystical looking suggestion, I will admit. It's practical and perfectly suited for the job. You can add divider tabs to keep the sections organized, and pages can be moved around without damaging anything. It's the best place to start.
Once you've chosen the format, take a little time to properly consecrate or bless your Book of Shadows so that it becomes a sacred tool instead of just a notebook.
What Goes in It
Only you can answer that. Ok, that's not very helpful. It is true though. Your BoS is a private book, much like a journal or a diary. You record whatever you feel is important in it. Some people may copy out charts of spell correspondences, but others might prefer to use a published book for that kind of research. You could use it to record spells you've done (and how they worked out), or may just spells you'd like to try some day. Recipes, Sabbat celebration ideas, poetry, dreams, Pagan history, God and Goddess information, and the list goes on.
If you decide later on that you've added things you don't need or want, just take them out. Your book should be an actively evolving project, not something set in stone.
If you're still looking for some spells from a real Book of Shadows, I have shared a few of my own. Don't be shocked to find they are just the same as any of the other spells here on the site.
Aside from the Book of Shadows, there are many other witch supplies that you may want to stock your altar with.
Famous Books of Shadows
If you are looking for ancient and "real" Books of Shadows, you are mostly out of luck. Even well-known books like the infamous Necronomicon will be a disappointment when you learn more about it.
But now we're just talking about other witchcraft books, which is another page entirely.