I have been here before, asking for a mapping library that could store objects in a database. Some one told me about the Core Data Framework. I have read a bit about it and
The book, More iPhone 3 Development begins with a great tutorial demonstrating how to use Core Data. I've found it incredibly helpful.
There's a tutorial on iPhone developer site here. And there are several sample codes with Core Data as well. These should get you started.
Here is a basic CoreData screencast that, while not specifically for the iPhone gives a decent introduction to CoreData concepts.