Pagination doesn't work on single.php

Hi, I’m new on wordpress theme development.
I’m trying to add pagination on single.php by adding this code.

<div class="nav-previous alignleft"><?php next_posts_link( 'Older posts' ); ?></div>
<div class="nav-next alignright"><?php previous_posts_link( 'Newer posts' ); ?></div>

But it’s not showing.

my single.php is like this:

`<div id=”content”>
<?php if ( have_posts() ) while ( have_posts() ) : the_post(); ?>

<article>

<h2><?php the_title(); ?></h2>
<p class=”small”><time datetime=”<?php the_time( ‘Y-m-d’ ); ?>” pubdate><?php the_date(); ?></time> – Written by <a href=”<?php get_the_author_link(); ?> “><?php the_author(); ?></a> – <?php comments_popup_link(‘Leave a Comment’, ‘1 Comment’, ‘% Comments’); ?></p>
<?php the_content(); ?>
<p class=”small”>Category: <?php the_category(‘, ‘) ?> &nbsp&nbsp&nbsp <?php the_tags() ?></p>
<?php if ( get_the_author_meta( ‘description’ ) ) : ?>
<?php echo get_avatar( get_the_author_meta( ‘user_email’ ) ); ?>
<h3>About <?php echo get_the_author() ; ?></h3>
<?php the_author_meta( ‘description’ ); ?>
<?php endif; ?>

<?php comments_template( ”, true ); ?>

</article>
<?php endwhile; ?>
</div>`

I try to put the code everywhere but it isn’t work.
Anyone can help?