¿maestra me podría prestar su libro? - "Could you lend me your book?" (We don't usually call our teachers "teacher" in English. Instead we say "Mrs. ____" or "Mr._______") se lo devuelvo mañana - "I'll return it tomorrow." es para fotocopiarlo/ sacarle copias..... ? - literally: "It's for photocopying it." In this context: "I want to photocopy it."

Could you let me borrow you book, teacher? I'll return it tomorrow. It's to copy photos from the copy machine.