Comments are good ways to pass feedback around in a team. You can add comment to an entire project or attach it to individual messages. However, to comment on other's projects, you need to be both a team member and a member of that particular project. To learn more about joining a team or project check out this article: Working with teams.
Add a comment to a message
While in the Flow Editor or Mock Editor, click on the Comment icon on top of the message title to add a comment to the message:
You can use the '@' symbol to mention a team member in a comment. They will be notified about the comment by an email.
You can add comments to any message and a message can have multiple comments.
Delete a comment
Click on the small trash icon under a message to delete it:
View, add or delete comments for entire project
While in the Flow Editor or Mock Editor, click the Comments button located on the top Project menu:
You will see a list of all comments in that project:
From this window, you can add a message to the project, delete any comment or click the link icon (a small box with a arrow pointing up) to jump to the message that has the comment.