First, do you know how to program in Java? If not, you must learn how to program in Java first (for the most part, all applications for Android are written in pure Java). Next, you must install and setup the Android SDK (the instructions for how to do this are on the official website).
Eclipse is, as far as I know, the only officially supported development environment for Android. You might look in to Unity, but I don't think that will be of much help if you do not have content of your own or serious programming skills (you don't mention whether or not you do):
http://unity3d.com/unity/publishing/android