Android SDK is a platform for developing applications and games for the Android smartphone operating system.
The Android SDK development kit includes all the libraries and attributes needed to develop, create and test applications for Android devices, and also facilitates testing applications that are being developed in another system.
For Android SDK to work properly you must also install a development platform. It is recommended to use Eclipse because it is the officially supported by Android SDK platform.
Android SDK includes everything you need to start developing applications and plugins, APIs, performance profiling, debugging tools and needed to use Java as a programming language. Furthermore, it supports most common media formats of audio, video and image, and enables reuse and replacement of components.
If you are new to application development or the first time you're using Android SDK you should read and internalize the tutorials, as the platform has many features. A big advantage is the online documentation available on Android SDK and over the Android developer community that can always help you out with any questions. In addition, the software includes examples that you can practice until you learn all the features of Android SDK.