Numbering the results

Adding number before each results

What is this, and where do I put this custom code?

add_filter( 'asp_results', 'asp_number_results', 10, 1 );

function asp_number_results( $results ) {
  $num = 1;
  foreach ($results as $k=>&$r) {
    // Modify the post title
    $r->title  = $num . ". " . $r->title;
    $num++;
  }

  return $results;
}