The Loop is PHP code used by WordPress to display posts. Using The Loop, WordPress processes each post to be displayed on the current page, and formats it according to how it matches specified criteria within The Loop tags. Any HTML or PHP code in the Loop will be processed on each post.

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

<div class="post"><!-- open the first div box -->

<!-- Display the Title as a link to the Post's permalink(Transformers 2 Revenge of the Fallen Official Movie Trailer). -->
<h2><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></h2>

 <!-- Display the date (March 11th, 2013 format) and a link to other posts by this posts author(admin). -->
<small><?php the_time('F jS, Y') ?> by <?php the_author_posts_link() ?></small>

<!-- Display number of comments(2 responses). -->
<p>This post currently has <?php comments_number( 'no responses', 'one response', '% responses' ); ?>.</p>

 <!-- Display the Post's content in a div box(Transformers 2 Reveng...bla bla bla). -->
<div class="entry">
   <?php the_content(); ?>
 </div>

 <!-- Display a comma separated list of the Post's Categories(Blog, Movie, Uncategorized). -->
<p class="postmetadata">Posted in <?php the_category(', '); ?></p>

<!-- Display Tag(Trailer, transformers). -->
<p><?php the_tags(); ?></p>

 </div> <!-- closes the first div box -->

<?php endwhile; else: ?>
<p><?php _e('Sorry, no posts matched your criteria.'); ?></p>
<?php endif; ?>

After we put the code in index.php we will see the code works like image bellow:
The loop result

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