WordPress comes with a comments system but many WP sites replace it with something else.
Why? Other comments systems can provide more features and more flexibility. Sites find that visitors prefer these alternative systems and that they help to encourage people to comment and become part of the site's community. This tutorial will show you how to set up perhaps the most popular alternative comment system which is from Disqus.com.
Video on Setting up Disqus.com Comments
Register at Disqus.com
Visit http://disqus.com and sign up for an account. You'll need to register the URL of your WordPress site.
Install the Disqus Plugin
Inside your WordPres site, install the plugin called Disqus Comment System.
The next step is to configure the Disqus plugin. You'll need to enter your Disqus.com username and password and then select the site you entered earlier.
If you've had your WordPress site for a long time and have existing comments, Disqus will then offer you the chance to migrate them.
Configure the Disqus Plugin
To configure the Disqus plugin, click Disqus under the Comments tab. When you've chosen your settings, Disqus will be ready for use on your site: