Build a Wikipedia Viewer please help

I don’t know how to find the api from wekepedia entry that is provided in this project .
I cheked it out many times ,but the explanation is not clear to me .
I don’t want to grab the api from someone’s work .
could any one explain to me what should I do in a simple way .

There’s nothing wrong with looking at other peoples work to get an understanding of how it’s done; in fact it’s encouraged. Just be sure to write the code yourself after looking, rather than just copying and pasting. The MediaWiki API in particular is kind of baffling, and definitely benefits from looking at working examples first.