(I think Lesson 3A is the most important but also the most difficult part for beginner so far ) This Notes is according to the udacity free course : Android Development for Beginners Lesson 3A : Object Oriented Programming Call Method on an objects If We want to call a method on an object object variable name . method name ( input argument ); ex: titleTextView.setText("News"); You need to make sure you put a right object so you can call the method