When you borrow a book, you can say: Can I borrow this book? May I borrow this book? ) or hi, I want to borrow this book. Hello, I want to borrow this book. )

When you return the book, you can say: Hi, I want to return this book. Hello, I want to return this book. )

Besides, how long can I keep this book? How long can I keep this book? Or if you want to study for two weeks, you can say: I like this book very much. Can I keep it for two weeks? I like this book very much. Can I keep it for two weeks? )

If you want to read more time, you can say: I think I need more time to finish reading it. Can I have it in the next two weeks? I think I need more time to finish reading this book. Can I keep it for two more weeks? )

Besides, if you want to copy the contents of a book, you can go up to the administrator and say, excuse me, can I copy something from the book? Hello, let me ask, can I copy something from this book? )

If you want the librarian to help you find a book, you can say: Excuse me, I'm looking for something about psychology. Do you know where I can find it? Hello, I'm looking for some books on psychology. Do you know where I can find them? )

Or: Excuse me, I'm looking for a book written by J.K. Rowling. Hello, I'm looking for a book written by J.K. Rowling

Or: Excuse me, I'm looking for a book called Star Wars (hello, I'm looking for a book called Star Wars).

Note: I'm sorry is the most common polite expression when talking to strangers. Chinese generally uses "I'm sorry", which can be understood as a polite greeting.