Each message within these topics is called a post.It's pretty simple, there's no need to use everything that's available, but... You can personalise your account with an avatar, a signature and more. You can send private messages to other users, have notifications emailed to you and attach files to your posts. You can embed links and other things (like youTube videos) in your posts. There are a whole host of options. If you want to explore the possibilities in more depth there is documentation here.
You might want to have a look at the control panel where you can set your options. You can specify what email notifications you'd like to receive here. If you want to be alerted by email when new posts are made in a particular forum then click the little tick at the bottom right of that forum's page, or to be emailed when a new post is made in a specific topic then click the little spanner just above the first post in the topic and select "Subscribe topic".
If you have any problems, questions or suggestions then let us know, either by making a new topic in the Forum Support forum, or by clicking on the little envelope icon at the bottom right of every page.