If you’re familiar with the loop, you’ll probably recognize the following code (or some variation of it):
<?php if(have_posts()) : while(have_posts()) : the_post(); ?>
<h3><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h3>
<?php the_content(); ?>
<?php endwhile; endif; ?>
In order to use the new post_class template tag, just be sure to wrap the content of each post that the loop outputs in a new div. The code would looks something like this:
<?php if(have_posts()) : while(have_posts()) : the_post(); ?>
<div <?php post_class(); ?>>
<h3><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h3>
<?php the_content(); ?>
</div>
<?php endwhile; endif; ?>