The library command is used to access a collection of books and references. The books are not guaranteed to provide accurate or update information, most will be written from the perspective of the author. What they provide is additional flavour and background information on builder content.
Typing lib help will show a list of valid commands. First find the book number you are interested in by typing lib list or lib search <keywords>. Once the book number is known it can be read by typing lib read <book number>