I started dabbling with building an app in Objective-C and Xcode recently. And Core Data seems to be a nice way to work with persisting data across app launches. But its learning curve is notoriously steep (Apple’s own documentation doesn’t help at all).
But Techotopia has a nice and short overview of what Core Data is and how it works in a way that’s not intimidating. But the best source for me by far is “Core Data for iOS and OS X with Simon Allardice” from Lynda.com. I’m a visual/audio learner. And the best way for me to learn is usually through a Youtube video or some clips from Lynda’s web site.