peteraloha on "Show Header Image on Front Page Only"

Alchemyth has already referred to this by proposing this code:

<?php if( is_home() || is_front_page() ) : ?>

YOUR CODE HERE

<?php endif; ?>

As newbie, can someone be a bit more granular with instruction: I am using a Child Theme in TwentyTwelve: *Where* specifically do I insert the code above?

Thank you to anybody that is willing to hold us newbie's by the hand as we tackle these very basic challenges.

Peter