Android is a software stack for mobile devices that includes an operating system, The Android SDK provides the tools and APIs necessary to begin developing applications on the Android platform using the Java programming language.

What is Eclipse?
Eclipse is an open source community which develops open platforms and products. and written in java By means of various plug-ins, it can be used to develop applications in various programming languages including Ada, C, C++, COBOL, Java, Perl, PHP, Python, R, Ruby (including Ruby on Rails framework), Scala, Clojure, Groovy and Scheme.

My first Android Apps Download format .apk