It would be as though there were multiple columns of post it notes, clearly illustrating the flow of the discussion. The on-line support group works the same way, except that the 'bulletin board' in this case is the computer. Each time a group member 'logs on' to the group, they communicate by leaving a message. All the messages are saved in the order that they are left, and follow the original posting to which it was responding. At any time, a group member can re-read any past messages, and take part in the conversation by 'posting' a message themselves.
Members can log on at any time, and 'post' as little or as much as they wish.
Things that are often discussed in on-line suport groups are medical issues, family concerns, how to cope with being ill, etc. The group members themselves decide what they wish to discuss, and new conversations can begin at any time. This can be a great benefit for someone undergoing cancer treatment, or who is too ill to travel. Groups also include some 'real-time' computer conferencing. Unlike the bulletin board messages, these conversations aren't saved for later, but they give group members a chance to interact with each other directly.