There are zillions of web sites where you can find useful questions & answers. From time to time I started to participate at some sites, but it never lasted more than a few postings. When I was new in iPhone programming, I noticed that most of the really helpful answers are at stackoverflow.com
It’s their sophisticated reputation and ranking system that leads to a self organised site where the best answer is most often at the top. If anybody finds an answer or question she or he can vote it up and the author gets 10 (5) reputation points. Silly questions like “Please write my code, I don’t know anything” and spam will be voted down and the author’s reputation goes down. When reputation exceeds 50, 100, … points the owner’s rights increase e.g. comment everywhere, reduce ads, edit questions, … 10k means access to moderator like vote for deletion, access to reports and more.
As a rule of thumb: The higher the reputation, the more reasonable the answer or question. It’s kind of Meritocracy in an easy but efficient way. It reminds me a little of Daniel Suarez great novel Daemon & Freedom (TM) (it is one story spread over two books).
There are more sites on stack exchange (59 in total) dealing with: