<?php

// Hook function with action
// add_action( hook_id, func_name, priority, number_of_arguments )
add_action('thesis_hook_before_post','recent_post_by_author',10,2);
function function_name ( $arg1, $arg2 ) {
  /* do stuff here */
}

// At the place of action
do_action( 'name-of-action', $arg1, $arg2 );