Apple.com Everyone Can Code - Everyone Can Code is Apple's comprehensive curriculum for learning how to code on iOS and Mac. Apple frequently adds new lessons, features, integrations, and tools to this resource.
In order to begin writing code for real applications, you must download Xcode from the Mac App store
Once you've installed Xcode on to your device, go ahead and view some of the resources below to begin building iOS applications.
"Swift is a programming language for creating iOS, macOS, watchOS, and tvOS apps. Swift builds on the best of C and Objective-C, without the constraints of C compatibility. Swift adopts safe programming patterns and adds modern features to make programming easier, more flexible, and more fun. Swift’s clean slate, backed by the mature and much-loved Cocoa and Cocoa Touch frameworks, is an opportunity to reimagine how software development works."
“This book describes Swift 4.1, the default version of Swift that’s included in Xcode 9.2. ”
About Swift - Playground - This playground is a great interactive tool that leads by teaching Swift in easily digestible chunks.
Ray Wenderlich: iOS Tutorials - These tutorials are a great place to find tutorials that show in-depth explanations of a specific framework (core iOS concepts, graphics and animation, maps and location, etc.)
Ray Wenderlich: Swift Tutorials - If you want to learn more about the Swift language itself, this page and the tutorials beneath are a great place to start.
Swift Education - This is an extension of the Swift Courses above, and "assumes instructor has read a book on iOS programming, has experience creating basic iOS apps and that the instructor is comfortable with Swift."