When abuse reporting is enabled, people will have access to a link through which they can report content as abusive. Content reported as abusive will be sent to a moderator's queue so that it can be evaluated. Abuse reporting is a system-wide setting — if it's enabled, it's on for every piece of content on which abuse can be reported.
Admin Console: Spaces > Settings > Abuse Settings
For more on abuse reporting and moderation, see Moderation Best Practices.