Welcome to Training for Android developers. Here you'll find sets of lessons within classes that describe how to accomplish a specific task with code samples you can re-use in your app. Classes are organized into several groups you can see at the top-level of the left navigation.
This first group, Getting Started, teaches you the bare essentials for Android app development. If you're a new Android app developer, you should complete each of these classes in order.
If you think you might prefer to learn the basics through interactive video training, check out this trailer for a course in the fundamentals of Android development.