Unhook Function in Parent Theme

I wanted to use the Remove Action function in a child theme of twenty thirteen.

But I wasn’t sure how to unhook the function properly. I don’t know what the $tag part of the function does and found the explanation a little more confusing… 

“The action hook to which the function to be removed is hooked. ”

So if we wanted to unhook the function twentythirteen_custom_header_setup

What is the tag? And what if the accepted_args?

remove_action( $tag, $function_to_remove, $priority, $accepted_args );

Here is the paste bin of the custom header function from twenty thirteen

<?php remove_action( $tag, $function_to_remove, $priority, $accepted_args ); ?>