Yes, I do know of the use of "Est-ce que" And changing the senctence VSO but, I get confused by sentences such as "Tu vas la bibliothèque aujourd'hui?"(Are you going to the libary today). When do you use this?
When asking questions, you can either use "est-ce que" or you can simply change the tone of a statement, as you did with "Tu vas la bibliothèque aujourd'hui?". If you get rid of the question mark, you lose the inquisitive tone, just as if you were to say "You're going to the library today(?)" in English