A Book of Shadows (BOS), or a Grimoire is a way for a a witch to keep track of their craft. More than that, it is essentially a journal of everything that a witch has learned, thinks is important, and spells that they have cast or intend to cast. It can contain affirmations of the way they live their life, details on the pantheon of deities that they call upon, uses for herbs and crystals, as well as pertinent information about various divination techniques. Suffice it to say, every witch will have different information available to them in their personal BOS. It is for this reason, that it is silly to think that another witch's BOS or grimoire will necessarily be relevant to your practice.
Coming out to the world as a Pagan or a Witch is often the most anxiety-inducing part about having an alternative path in life. Never fear, it's not mandatory to come out and if you prefer to keep your practice to yourself, that is most certainly your choice. Never let anyone tell you that there are mandatory requirements in your practice, because what works for you, is for you, and you alone to decide.