Documentation: Enrolling in the iOS Developer Program
Intro to Xcode 4.3 by profgustin
Documentation: Creating an XCode Project
Documentation: Custom Icon and Image Creation Guidelines
Check out an excerpt from lynda.com about Launch Images:
Geeky Lemon Development has a video tutorial about making and uploading App Icons for retina and non-retina devices:
Gimp is a great image editing program. You can download it for free from gimp.com.