[Kim]

How do I put a <–Previous / Next –> on the bottom of all my posts?

[Sakin]

@Kim: In this theme Previous and Next will be at the top of the post. But you have hidden it by adding the following css. You can remove that and it will load at the top of your post.

.single #nav-single {
    display: none;
}

To move this at the bottom, you need to build child theme. See this http://catchthemes.com/blog/create-child-theme-wordpress/ and then copy single.php file in your child theme and then move the code

<nav id="nav-single">
	<h3 class="assistive-text"><?php _e( 'Post navigation', 'catchbox' ); ?></h3>
	<span class="nav-previous"><?php previous_post_link( '%link', __( '<span class="meta-nav">&larr;</span> Previous', 'catchbox' ) ); ?></span>
	<span class="nav-next"><?php next_post_link( '%link', __( 'Next <span class="meta-nav">&rarr;</span>', 'catchbox' ) ); ?></span>
</nav><!-- #nav-single -->

Below:
<?php get_template_part( 'content', 'single' ); ?>

[Author]

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