On your browser, navigate to http://developer.android.com/sdk/index.html; the website should present you with a download link to the appropriate Android Development Tools (ADT) bundle. The web page automatically provides a proper version for your working platform, and thus downloading and installing it is a fairly straightforward process.
Tip
If you already have an existing Eclipse installation on your machine, you can also save some disk space and download only the ADT part from the same page. The installation process is slightly more complicated in this case, but the instructions on the web page can help you with that.
Open the ADT bundle (or the Eclipse environment) that you've just installed. Before we start a new project, you will most likely have to download an SDK that is suitable for your particular device. In our example, we will be using Android 4.0 (code-named "Ice Cream Sandwich"). However, we will avoid using any recent APIs; so if you have an existing...