Any time someone comments on a post that you distributed through Oktopost, it will appear in the Social Inbox. Regardless of the network you posted to, this feature will collect all of your comments, and also enable you to reply to them directly from the interface.
To use the inbox simply head over to the Inbox tab in your account. Posts with unread comments will appear in white while read comments will appear in grey.
To leave a reply simply type the reply on the form that appears below the post. Please note that your reply will be posted using the profile that was used to originally post the message.