Like every iteration of iOS, iOS 9 brings forth a lot of new features. UIKit changes with every release of iOS, but one particular addition in iOS 9 will change how developers fundamentally think about creating user interfaces on iOS, UIStackView. In this tutorial, you will learn how to use UIStackView to create user interfaces.
Starter project for the Tuts+ tutorial: iOS 9: Getting Started with UIStackView
Read this tutorial on Tuts+