It is libraries if you are talking about more than one library.It is library's if you are talking about something that belongs to one library, such as the library's entrance.It is libraries' if you...
The difference is in the punctuation. Library's is possessive. For example, you would use this form to say, "There was a cat sitting inside the library's book-shoot." Libraries is plural. For...
the role of a library is to teach or make someone learn something.the function of alibrary is to keep library clean and tidy and arrange all the books in a orderally way