Librería vs. biblioteca
The Spanish words librería and biblioteca are a classic example of false friends for English speakers. Although librería looks like library, their meanings are quite different and refer to distinct places related to books.
Librería
A2A librería is a retail store where you buy books. It is the Spanish word for a bookstore or a bookshop.
Fui a la librería a comprar la última novela de mi autor favorito.
(I went to the bookstore to buy my favorite author's latest novel.)
¿Sabes si esa librería vende libros de segunda mano?
(Do you know if that bookshop sells second-hand books?)
Mi hermana trabaja como vendedora en una librería del centro.
(My sister works as a salesperson in a downtown bookstore.)
La nueva librería tiene una sección infantil muy grande y una cafetería.
(The new bookstore has a very large children's section and a coffee shop.)
Necesito un mapa de la ciudad, seguro lo encuentro en esa librería de la esquina.
(I need a city map, I'm sure I'll find it in that bookstore on the corner.)
Biblioteca
A2A biblioteca is a place where you can read and borrow books, usually for free. It is the Spanish word for a library.
Tengo que devolver estos libros a la biblioteca antes del viernes.
(I have to return these books to the library before Friday.)
Los estudiantes se reúnen en la biblioteca para estudiar en silencio.
(The students meet at the library to study in silence.)
Para sacar libros, primero necesitas un carné de la biblioteca.
(To check out books, you first need a library card.)
La biblioteca nacional tiene una colección de manuscritos muy antiguos.
(The national library has a collection of very old manuscripts.)
Mi abuelo donó su colección personal de libros a la biblioteca del pueblo.
(My grandfather donated his personal book collection to the town's library.)
Summary
In short, the key difference is commerce versus lending. You go to a librería (bookstore) to buy books, and you go to a biblioteca (library) to borrow them.