Suppose you found a magic book in which the pages are blank
The book, is magic like I said. If you write in the book, whatever you wrote in it will come to pass in some way, shape or form no matter how crazy it is.
If you take notes in it or write reminders, you'll never forget them
If you draw in it, whatever you drew in it will come to life, its behavior is based on your mind and what you think of it
So let's say you drew a JP Velociraptor, unless you think about it in a different way, the book will just make it act like a typical JP raptor based on your knowledge about it, unless you willing or unwillingly think about it in a different way
Like you imagine a raptor with the attitude of a 5 week old Puppy
Or you could also draw that trait somewhere and it'll act like how it's depicted, draw a dinosaur fetching a stick or eating out of a dog dish and you'll have a Dinosaur that acts like a dog
Also if you write in the book, a description, or a noun, it'll manifest that to.
If you erase anything you draw in the book, it vanishes, with stories or other things, you gotta erase before it comes to pass
If you write and or draw in pen, it's permanent, unless you have an erasable pen
In terms of the book's origins, IDK
Could have belonged to some sorcerer or witch
Could be Extra-dimensional
Could have belonged to death and he just left it
All that matters is now, you have it