How to show the latest blog post on the sidebar

Open the sidebar.php file and paste the following code....

<?php query_posts("post_per_page=1"); the_post(); ?>

<div>

<p> <?php echo the_date(); ?></p>

<h4><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h4>

<p><?php the_excerpt(); ?></p> 

</div>
 <?php wp_reset_query(); ?>