Conferencing is asynchronous - in other words discussions are not 'live' and do not depend on participants being connected at the same time. Generally this is not the case. Be aware that any messages you post may be read by anyone. Periodically discussions will be managed. This means that moderators will decide that there are either too many messages, some messages are out of date and or messages are not relevant or helpful.
Messages can therefore disappear.
Usually a moderator will give a week's notice before a radical clean up. If there's useful information in a Seminar discussion it is best to note it down when you see it rather than relying upon it being there next time you visit. There are various Seminar discussions. Discussions may be divided into sub-topic discussions. There are various ways of reading the discussions.