In Hollywood, the book of shadows has had some over-the-top exposure. Some were even composed of human flesh! But, in real witch life, this book is so much more than a creepy book of spells.
The book of shadows is the reference book practitioners of witchcraft use. In some cases, a person can possess this book without needing it for magic at all (depending on the owner's path). It is the go to source for all things, and anything, witch (or Pagan). Of course there are spells, but there is so much more! What is included in your book is entirely up to you. It's your document; it's your rules!
The life of a witch is filled with a plethora of subjects, ideas, and information. There are deities and rituals. Every deity has his (or her) own characteristics. And every ritual carries its own requirements. Then, for strong magic, the practitioner has to know what color corresponds with what intent (or emotion, or goal). Magic (otherwise spelled as magick) is more than performing spells. Unlike Hollywood's depiction, it takes much more than some random rhyming words and a pointed finger to perform any spell. Thus, having this book is not only about performing spells, or a gathering of spells. It is all the information a witch may need to, not only carry out spells, but live as a witch. The author may record anything that he, or she, feels is important to their well-being, their growth (either personally or spiritually), and other aspects of his or her life. Magic is a lifestyle, not merely a practice.
For example, many practitioners hold the moon in high regard. Every phase of the moon is associated with important information (such as which activities to perform or avoid). It corresponds with, not only spells, but certain rituals, focus, and other attributes someone practicing magic would like to know. Some would, then, choose to have moon phases (in varying detail) in their personalized reference book.
Others may choose to include a section on herbs. Herbs are useful as natural remedies, so this section of the book could include a homeopathic cough syrup, or a natural antiseptic. They also correspond with elements of casting a proper spell, and have many other benefits. Still, others may choose to include instructions on how to make their own candles, or how to meditate.
Many people who practice believe that this personal guide should be kept confidential. Others will share with a student, or someone who wishes to learn more. It is usually a personal document, however. And, as with many things in the world of the witch, it should not be touched by anyone (other than the rightful owner) without permission!
Depending on the personal path, the information included will surely vary. When composing your own reference book, anything and everything goes. You can have a hard copy, or a digital copy, or both. There are very few rules. If it speaks to you, it should be included. It is the witch's own, personal guide.