English question, please help.?

Conversationally, this is perfect. If this is for an assignment for a teacher that is very picky about using complete sentences and proper grammar, you could also say "It's over there" without sounding too awkward. Don't say "It is over there" - It sounds very forced to use so many words for such a simple point.

The library is over there is more formal and grammatically correct however, that would be fine in conversational speech.

Well, if you were using that in a conversation, then it's okay. However, if you want to be more descriptive, you will say It's over there

That's fine! :)

It really depends on the context of the conversation. But when in doubt I would suggest saying "It is over there."

It is over there

or The library is over there. Would be fine too.

If you want to be more precise and answer in a complete sentence, you could say, "The library is over there." If you're just having a casual conversation, you could just say "over there" but I would prefer saying "it's over there" because it's more of a complete sentence.

That's fine.