Sardon, the Activity area is basically the public message board, viewable by all. Here is a link found under the category “Help - Computer &System” that will explain the workings of the Forum.
https://tab-rv.vanillacommunity.com/discussion/9412/how-to-navigate-the-t-b-forum-essential-for-new-members#latest
Please note to never use the large Activity box on your own account profile page as you only send a message to yourself. That message area is to be used to send another member a message via their profile page. To communicate with the group, go to the Home page and start a New Discussion. Or, add your comment to an established thread.