Jetpack Comments replaces your default comment form with a new comment system that has integrated social media login options.
You can turn Comments on by enabling the “Comments” module from the Jetpack tab in your Dashboard.
We're breaking down the barriers between you and your audience. When someone reads an article on your site and wants to comment, they can now use one of their existing social networking accounts to post a comment. No longer do they need to create yet another account and profile.
Since it is a large change, we are making Jetpack Comments opt-in. To activate it, just visit the Jetpack menu on your Dashboard and click the Activate button inside the Jetpack Comments box.
When activated, Jetpack Comments takes the place of your theme's comment form in this nifty, sleek form:
To leave a comment, just click in the box and start typing.
After a visitor has written a comment, they will have several ways to identify themselves. A visitor can leave a comment as a guest¹, or they can choose to use their WordPress.com, Twitter, or Facebook account. For example:
You can also change the "Leave a Reply" heading and the color scheme of the Jetpack Comments form under the Settings → Discussion menu.
See our Troubleshooting Jetpack Comments page for some help.
¹ Guest commenting is still controlled by the options in Settings → Discussion; if you disable guest commenting, visitors will not be able to use this option in Jetpack Comments.