Each post and PM has a report button (flag icon) at the bottom of it. Click that button and type in the reason for the report in the pop-up that appears. Then, click the "Submit Report" button to let the moderation team know what's happening.

If there are multiple posts with the same issue in the same topic, there's no need to report each individually. Use the report button on the first post and indicate in the report reason that it is one of several. Please remember to include the reason for the report with as much detail as possible.