If you want your blog to support comments, follow this:

Octopress has a native 3rd party plugin for Disqus that will host all your blog’s comments.

Visit http://www.disqus.com web site and sign in, Then https://disqus.com/admin/signup/.

Here’s example how I file the signup form my blog which is hosted in GitHub pages.

Site Url: asaf.github.io
Site Name: Asaf Shakarchi's Blog
Site Shortname: asafshakarchisblog

Remember the site short name, you need it soon!

Then configure Octopress to be aware of your new Disqus application:

cd octopress #or wherever your octopress folder is located
vi _config.yml

#then change discqus_short_name line:
disqus_short_name: asafshakarchisblog #replace with the short name you've put in the app signup form

Done!