When you create an account, you provide your site URL. It is important to understand that if you are developing or testing your site on a server other than the one registered with your domain name, the Disqus comment section will not appear. So if you are setting things up on your local machine and testing, you will not see the full comment section. Once you push your code to production, you will then see the full Disqus comment section.
That is it...it is very easy to set up and use...