Apple Developer. Single Shared UIManagedDocument. Note: This post is a bit out of date these days and I'd now recommend using a "standard" Core Data stack over UIManagedDocument whether you're planning on using iCloud or not.
Many of the Xcode templates come with a basic Core Data setup to help you get started. I've also put together a very small library, a Core Data In-A-Box if you will, you might also find useful.