Any suggestions on how to approach learning Cocoa Touch API?

I am an experienced programmer (C, a bit of C ++, PHP, JavaScript) who is immersed in iOS development. I must say, although I get Objective-C without any problems, the Cocoa Touch API is massive and quite complex. Things that seem like they will be simple, like dropping an annotated pin on a map, require a few steps that I would never understand without reading an example in a book.

I am looking for suggestions on how to handle learning about this Behemoth API. Let's say I wanted to figure out how to open a URL, extract XML data from it, and parse it. How in the world would I even know where to start (just an example, I really do not answer this)? I have Xcode 4, so I believe that the documentation should somehow make this relatively simple for me. I'm just new to this, so I don't know where to start, so any advice would be stellar. Thank.