For an absolute beginner a good way to start is by following an online course in iOS development:

http://www.hackrocket.com Will soon launch an immersive three-month program to teach absolute beginners how to build iPhone and iPad apps

http://teamtreehouse.com/

http://www.lynda.com/iOS-tutorials/iOS-SDK-Essential-Trainin...

http://itunes.apple.com/itunes-u/ipad-iphone-application-dev...

http://codelesson.com/courses/tag/Mobile

You can also try to learn on your own. Here are some of the best books:

- iPhone Programming : The Big Nerd Ranch Guide

- Cocoa Design Patterns

- iPhone App Development : The Missing Manual

- The iOS Developer's Cookbook

- Cocoa Design Patterns

- Head First: iPhone Development

Once you start developing http://www.stackoverflow.com is an invaluable resource

Ray Wenderlich's tutorials are really great:

http://www.raywenderlich.com/tutorials

Here's one specifically for High School students:

http://www.raywenderlich.com/5600/ios-for-high-school-studen...

And another, creating a text adventure game:

http://www.raywenderlich.com/11079/ios-for-high-school-stude...

And here's Apple's:

http://developer.apple.com/library/ios/#DOCUMENTATION/iPhone...

There are bunches out there, though--would love it if you report back later on what your favorites were!

I am busy working through the Big Nerd Ranch books and so far i am VERY impressed