Apple's document organization assumes that you start at the beginning and establish a strong basic understanding of the frameworks, patterns and naming conventions. Once you have that, the docs tend to be extremely easy to navigate because you can almost always guess what a thing is called and how it would work if it existed. If you try to jump into the middle and find how to do just this one thing, then they do tend to be confusing because iPhone development is much more about placing your code in the right place than knowing the right thing to call.
As has been noted, these specific things are private. Once you have a good understanding of the iPhone frameworks and design approach, it will tend to also be obvious what is likely private. Anything that messes too much with the hardware, and definitely anything that could prevent the user from receiving a call, is likely to be private. There are a lot of things that Apple will likely make public over time. Modifying the 3G network settings will never be on that list.
And as has been noted, including these features (especially features that modify network settings), can definitely get you removed from the App Store. Screen brightness (as a setting applicable only when your app is running), may be available someday, though I expect it will be a single dim/bright/off setting. Again, Apple is unlikely to allow you to modify the screen brightness in a way that persists outside of your application. Apple will likely never allow developers to do things that can interfere with making phone calls.
If you're having trouble with the docs, I recommend starting with Cocoa Fundamentals. It's not a skimming document. It's definitely a read-ever-word, do some development, and then come back and read it again kind of document. Cocoa is not just Java with a different syntax. It does take some work to understand the patterns. But once you do, it's a really beautiful framework. I discuss a lot of learning Cocoa issues on Cocoaphony if you find yourself looking for more information.