The document discusses the key building blocks of Android applications. These include Activities, which represent visible screens; Intents, which are used to invoke components like starting services or launching activities; Services, which are background processes that can run for a long time; Broadcast Receivers, which receive and respond to broadcast announcements; and Content Providers, which expose and manage access to application data. Additional components include Views, Layouts, and the Manifest file. The document also covers notifications and resources in Android.