What is the difference between a card and a comment?
Cards are created by organizers (group owners, leaders, or administrators) and appear on the board along with comments from group members. Cards have a title, and may have richly formatted text content, documents, images, a place, and / or a time. In addition, cards may contain action items, which are tasks that members of the group are expected to complete, and things for which members may signup to do or bring. Cards can also be searched and visualized in a variety of useful ways, for example, on a calendar or on a map.
Comments are posted by members or organizers to the board. They only consist of text and/or images and are visible to all members of the group.