First your need to install ADT (Android Developer Tools).
- Unpack the ZIP file (named adt-bundle-<os_platform>.zip) and save it to an appropriate location, such as a “Development” directory in your home directory
- Open the adt-bundle-<os_platform>/eclipse/ directory and launch eclipse
ADT (Android Developer Tools) is a plugin for Eclipse that provides a suite of tools that are integrated with the Eclipse IDE. It offers you access to many features that help you develop Android applications quickly. ADT provides GUI access to many of the command line SDK tools as well as a UI design tool for rapid prototyping, designing, and building of your application’s user interface.
Instead of ADT you can also download the SDK Tools, but the SDK Tools package is not the complete SDK environment. It includes only the core SDK tools, which you can use to download the rest of the SDK packages (such as the latest system image).