A book is a collection of bound pages. They are used for reading. Books can range from useful (encyclopedias, dictionaries, phone book, crush's diary) to filler (Playboy, Harry Potter) to just plain useless (Twilight, Glenn Beck). Books are almost never written in Simple English. The master of Simple English books was Dr. Seuss, but he died.
Books were invented by Jews, who published the Torah. After that, some other holy books came out and then were replaced by crappy bargain romance novels.