First Sim needs to go to Library and talk to Librarian to sign in. Then each time they want to borrow a book, they first need to talk to librarian. Librarian is available in the library only during the day (I think between 8 am – 10 pm? ).
This is a career mod, This mod starts off with Trust Fundie and from there you can branch off into "daddy's favorite" Or decide to work for your family's business and eventually become the CEO, or you can be an entertainer managed by your family's business.