After you send your mailing, you may decide to follow up with those folks who opened, clicked a particular link or bounced. You can easily target those people by saving them as a segment.
On your response overview, click the tab for those you want to target.
Near the top of the page you're taken to, click Save this tab as a segment.
Use the pre-filled segment name or customize your own -- either way, it'll be saved on your Audience page for easy reference and sending.