Most forums usually have a button above a post where you can report the post to a moderator or admin, and then the staff member reviews the post and determines what the problem is with it. If there's no problem with the post, no action is taken. If the post breaks a rule, the staff member decides the course of action to take. It's pretty simple. Though, it would be against the rules to troll someone by constantly reporting their posts even if there was nothing wrong.