One of the more confusing parts of the BGG API is the fact that there are two of them. Some of the material in the original API is still relevant because it hasn't been implemented in the newer API. If you find it difficult to complete a certain task in BGG API2, check API1, because you might be able to do it there.
Another issue with the API is that you can't easily do something like get a listing of the top 10 games on BGG. To do so requires you to do some web scraping which is out of the realm of this how-to guide. For more information on how to do something along those lines, check this thread to see how other users have done it.