What is the difference between "に" and "には"?

Question

The title should be pretty self-explanatory. What meanings does each convey? And in what kinds of circumstances would one be used instead of the other? For example, what are the differences between these two sentences? > 図書館に本がある。 > 図書館には本がある。

Answer 1

The place is both the topic AND location.

図書館に本がある。There are books at the library. (statement of fact)

 図書館には本がある。Speaking of the library, there are books there. (highlighting a difference, new information or very key piece of information)