What is Android?
Android Operation System
Android is an operating system based on Linux with a Java programming interface.
The Android Software Development Kit (Android SDK) provides all necessary tools to develop Android applications. This includes a compiler, debugger and a device emulator, as well as its own virtual machine to run Android programs.
Android is currently primarily developed by Google.
Android allows background processing, provides a rich user interface library, supports 2-D and 3-D graphics using the OpenGL libraries, access to the file system and provides an embedded SQLite database.
Android applications consist of different components and can re-use components of other applications. This leads to the concept of a task in Android; an application can re-use other Android components to archive a task. For example you can trigger from your application another application which has itself registered with the Android system to handle photos. In this other application you select a photo and return to your application to use the selected photo.
Developing Android App
To develop android app you need some tools
1. Download android SDK from https://developer.android.com/sdk/index.html
2. Download eclips from https://www.eclipse.org/downloads/packages/eclipse-ide-java-ee-developers/junosr2
3. Download PhoneGap package from https://phonegap.com/
I will show you how to configure all of that but for now just download all the tools you need. keep it in mind i am using windows for this tutorials so if you are using Linux or Mac than your interface might me little different than mine. but the main coding part is same.
So keep looking on that site and ready to be a android developer. Have Fun