Comments appear in the right side of the page under the task detail pane. Any team member with access to the task can view the conversation and offer a comment. Followers are immediately notified on a new comment.
Comment on a task whenever you want to discuss work with your team. Comments keep your communication in context of the task and is always available for reference purposes at a later date.
So, never forget to comment when you have an update, more information or insight to share!