Disqus is a worldwide blog comment hosting service for web sites and online communities that use a networked platform.
It will allow your site users post comments on blog pages.
In order to configure it, click on Connect with Disqus
Once you click on that, system will redirect you to a separate page, to connect you to your existing Disqus account, or create a new account:
You will be able to manager your comments in admin> Blog> Manage Comments link. In case if it Disqus plugin is not configured, Manage Comments link will rediret you to this plugin's configuration.