This tutorial demonstrates how to integrate calls into an iOS application using a custom UI component called NXMCallButton, which is a subclass of UIButton. The button can be configured to call either in-app users or PSTN numbers. To complete the tutorial, you need a Vonage API account and a virtual phone number. The project uses CocoaPods for dependency management and requires microphone usage permission. The NXMCallButton component can be added to the user interface using either Storyboard or programmatically.