Android SDK

It consists of the following:

• Android API: The API libraries provides the developer an interface to the devices in-built functions. Its the same libraries google uses to develop their native apps. As each api update release happens for your android handset, the SDK manager also receives updates, so that the developer can use the latest apis to built more featured applications.
• Development tools: These are tools to compile and build executable applications out of the written source codes.
• Android Emulator: In order to run and test your applications during the development phase, the SDK provides you a variety of emulator types. Using this you can get a visual experience of how your app runs in different devices. 
• Sample codes: The SDK manager also has a huge collection of sample codes which describes on how to use different apis for different development needs.