Disqus comments plugin will add a disqus comments section below every blog post.
You will need a site shortname provided from Disqus. To get it go to https://disqus.com and follow instruction to create a new site.
Then on https://disqus.com/admin/settings/general/ you can get the site shortname
Note: Your selected theme must include the post.after widget_area. To include it in the theme, in single-post.php add this line just after the post output.
<?php view::widget_area('post.after'); ?>