Read all the following tutorials :
http://www.raywenderlich.com/20881/beginning-auto-layout-part-1-of-2
http://www.raywenderlich.com/20897/beginning-auto-layout-part-2-of-2
http://www.techotopia.com/index.php/Working_with_iOS_6_Auto_Layout_Constraints_in_Interface_Builder
http://www.adevelopingstory.com/blog/2013/05/auto-layout-for-ios-revisited.html