Looking for guides on programming in Objective C on OSX
I'm going to say "google it", but I don't mean it to be a brush-off of your question. I learned Objective-C primarily with Google and the wealth of information it provided. Apple has good documentation, but plenty of other blogs and articles are out there that explain parts of the language better than Apple. I'd start by looking for an Objective-C primer or, if you are familiar with another programming language, a document explaining how that one compares to Objective-C.
Once you have the basics down, then start looking at the more advanced topics you will need, like delegation, making classes, method declarations and calls, the compiler directives Apple uses, ARC, and so forth. Again, I'm not going to offer specific links because what made sense to me may not work for you, and vice versa. The best thing is to google a specific question or statement ("basic syntax of Objective-C", "how to make a class in Objective-C", and so forth) and find the resource that works for you.
The other suggestion I have is to take a look at all the Apple-run email lists and join one or a few. Specifically, the cocoa-dev list should be quite helpful.
I do want to clarify one point: Cocoa and Objective-C are not the same thing, though people will often use them interchangeably. Objective-C is a language, like C++ or Python. Cocoa is a framework built using Objective-C that provides the main interface to the Mac environment for app developers (Cocoa Touch does the same for iOS).
Once again, I don't usually tell people to google their questions. In this case, though, Google is going to be your primary resource, at least it was for me (and still is, actually). Please don't take my response as me blowing off your questions - I don't mean it that way at all. Best of luck, and come back here if you have additional questions.