To get started you need Android Development Tool (ADT) Bundle from Android Developer website and the latest version of Cordova. Then follow the installation instructions and the getting started guide for Android. Depending on what kind of setup you are on, if you do not have admin access to run the command line, you need to follow the previous version of the getting started guide or read this post from Simon MacDonald.
Once you have everything installed, you might want to run the SDK manager from inside ADT to get other versions of the Android SDK. One thing, though, do not forget to during the setup to also follow the instructions for modifying the manifest file as skipping this step could cause your app to crash straight away on starting.