What is the difference between an announcement and a comment?
Announcements are created by organizers (group owners, leaders, or administrators) and appear on the feed along with comments from group members. Email announcements have a subject, and may have richly formatted text content, documents and images. In addition, announcements may contain action items or events, which are tasks that members of the group are expected to complete, and things for which members may signup to do or bring.
Comments are posted by members or organizers to the board. They only consist of text and are visible to all members of the group.