the first place you should go is android developers' website : https://www.google.com/url?q=http://...LJXUmICi3s2HUA
but of course you will first have to learn java (xml,sql as options) :http://www.freejavaguide.com/corejava.htm
if you already have some linux knowledge it will be of good help to understand how android realy works , i know it souds stupid but you should first of all start from wikipedia to find out more about android : http://fr.wikipedia.org/wiki/Android
for learning there is also Android IDE (free) that you can find on play store it is an ide for android that works on android , you can find on play store also some references about java programing language and tutorials for begining android development , ps: you can also make apps with phonegap if you are already a web developer , but i dont advice you to use phonegap for heavy projects as you dont have full control of the performance : http://phonegap.com/developer/
note that a version of phonegap on play store that works on android (paid) , it is made by the same team that made AIDE , dont forget about html5 apps also (they are multiplatform but need a browser with html5 support) , i hope i helped you .