customizing twenttwelve

I am trying to create a custom child theme of twentytwelve. I’m stuck on a part to customize the data under the excerpt on my homepage. What I’m trying to do is add a list under the excerpt that uses images for links:
Add Comment (Image) – Read Full Post (Image) – Share This (image)

what file would I look in to customize this layout?
Not sure if this is related but I created a custom home content page content-home.php and changed ( 'content', get_post_format() ); ?> to ( 'content', 'home' ); ?> when I did this I got an error saying the <?php twentytwelve_posted_on(); ?> function was not defined but when I revert back to ( 'content', get_post_format() ); ?> there are no errors.