Witches seem to always have magic books. 

Your personal grimoire, or "Book of Shadows" can be as many volumes as you want it to be. Many witches keep different books for different things, such as magical diaries, rituals, spells, recipes, dreams, etc.

There is no hard and fast rule about your book. You can use anything you like from the most ornate to a simple binder.

It's wise to always remember that however you do it, keeping good notes is essential to successful magic, and keeping your Craft private and away from prying eyes gives it more power.