what should I add to not duplicate the featured post with posts the loop below the featured section?
particular the section after the headline 'Note for Multiple Posts in the First Category'
i.e. using an array for
$do_not_duplicate and the
'post__not_in' parameter in a query for the rest of the posts.
example - assuming that you have the post ID of the 'featured' post in the
$args = array_merge( $wp_query->query, array( 'post__not_in' => $do_not_duplicate ) );
query_posts( $args );
you could also paste the full code of your category archive template (into a pastebin ...) and someone might have a look at your code.