The Android SDK has the tools, sample code, and docs you need to create great apps.
Here´s an overview of the steps you must follow to set up the Android SDK:
Prepare your development computer and ensure it meets the system requirements.
Install the SDK starter package.
Install the ADT Plugin for Eclipse (if you´ll be developing in Eclipse).
Add Android platforms and other components to your SDK.
Explore the contents of the Android SDK (optional).