BECOMING ADEPT AT Android programming is a book in its own right. However, there is little more than the concise Google documentation available on the topic of the Open Accessory standard.
In this appendix, it is assumed you have a basic familiarity with Android and Arduino programming, but want to understand how the Open Accessory apps used in many of the projects work.
There are many good books on the subject of learning Arduino. Buy one and work through at least the first few chapters to get an understanding of key concepts like Activities and Intents, as well as how to set up a development environment and use the Java programming language.
Many web resources and tutorials are available ...