To enable Disqus commenting, all you have to do is supply your Disqus Shortname. If you don't already have one, you can sign up for a free account over at Disqus. They'll give you a Disqus Shortname, and all you need to do is pop it into the appropriate field in your blog's customization sidebar.
If your theme allows Facebook commenting, just follow these steps to get it working:
- First, head to the Facebook Developers site, sign up, and click on Set Up New App.
- Input any name you'd like for your hypothetical app (you're not actually making one, dont' worry), agree to the ToS and click Create. You're almost done!
- Input your Contact Email (in Basic Info) as well as your blog's URL into the "Site URL" box (in the Website tab) and save your changes.
- Copy the App ID located just below your app’s name and you’re all set. Now head back to your blog and input your App ID into the “Facebook API ID” field in the customization sidebar, and make sure you’ve checked “Facebook Comments On.”