Excluding Category

Hi All,

I am creating a new page template.

The idea is to show only blog posts in a certain category or exclude a certain category.

<?php if(have_posts()) : while ( have_posts() ) : the_post(); ?>

				<article <?php post_class('mix'); ?>>
					<?php if ( has_post_thumbnail() ) { ?>
					<div class="image">
						<a href="<?php the_permalink(); ?>" title="<?php the_title_attribute(); ?>">
							<?php the_post_thumbnail('blog-type-1'); ?>
						</a>

I have seen a few options on here but am a bit confused which one to use;

<?php query_posts($query_string . '&cat=-4723'); ?>

Thanks

Josh