A Book of Shadows contains all the information a witch or wizard could want, no matter what tradition or path he/she follows. It is used as a giant encyclopedia of information for that personal person. Some Book of Shadows contains spells, rituals, herbs, etc, while others are used as religious texts (much like the Christian Bible) which contains the core rules, ethics, philosophy, and magical practices of a coven or solitary witch.
What goes in a book of shadows
There is no rules about what does and does not go into your BOS. However you should not use it to record mundane bullshit. This book is part of your magickal tools and should be used for that.
eBook of Shadows
Some, like me, type it out on the computer or even post it online. I prefer this method since I can add things at will and it still can be edited. I can organize it as I go and I don’t have to shuffle tons of pages around in the process. I just press enter and add a new entry or press backspace and delete what I was writing in case I mess up or decide I want to word things differently.
Paper Book of Shadows
Starting out, don’t run out and buy the deluxe binder with folders, dividers, and such. You could change your mind. Instead take a note book, one subject or whatever and begin writing in it (Be sure to have this 3 ring binder capable though, it saves time if you change your mind later on).
Some people like to use a 3-ring notebooks so pages can be added, removed for easy use during rituals and reorganized easily. Try to find a quality 3-ring notebook so it lasts for a while (cheaper one tend to fall apart quickly.) when the note book needs replacing the pages can be transferred easily.