What is Android ?

Android is an operating system used to develop mobile operating system. 
android is an open source operating system developed on linux.  android uses the kernel of linux to to access the hardware.
at present android support java language for programming. later on there may be a chance of android programming in c or c++.
to start development you need to use eclipse as editor and download the android sdk from android official website.  although you can use other editor it will be easy to configure and develop application in eclipse.
before starting development you must have knowledge of java programming language.