The book is an useful tool which you can buy because it contains a lot of information about a player. The books knows everything about a player. But they are difficult to read which means that you need to stand in front of a player to get the information about him.
It is also an important tool for the cops to see if a person is criminal or how much money he carries around with him.
If you want to get information about a player you need to rightclick him with a book in your hand. Now you get a few player details for example: If he is cop or robber, how much money he has, the onlinetime and his mininglevel. You can get more information about the mininglevel in our article about mining.
You can buy books from the "Snacks" Shop at the Spawn.