Before you begin,
You must know basic programming language like JAVA because android is most base on java.
secendly you must have a little bit expireence on XML.cos these two are significient for ANDROID programming,
Lets start........


step 1:
download java development kit(JDK) from oracle site...here is the link
www.oracle.com/technetwork/java/javase/downloads/index.html

install it into for your windows mac or other operating system..here i am using 4 windows .
see how to install JDK 

step 2: 
download eclipse 
and install it
see how to install eclipse



step 3: 
download sdk for android 
http://developer.android.com/sdk/index.html
download windows or linux version of android according to your operating system..i am useing
installer_r15-windows.exe (Recommended)
see how to install sdk for android


This site is