How do you create app icons for iOS?
App Icons are the nice, neat little wrapper for your app. They’re usually the first thing that users see before using your app, and they’re a constant reminder to your users of your app and your brand. In this screencast, we will show you how to design an app icon that shows off your brand, and fits in nicely with other app icons on the Home Screen.
For the More Curious...
App Icon - Icons and Images - iOS Human Interface Guidelines
Sketch - The digital design toolkit