Although you can view some posts as a guest, please login always to make sure you can access all the board features. Once you have logged in you will be able to identify which all posts you haven't viewed before.
The messages you have read before are marked by topic_read where as unread messages are indicated by topic_unread.

You may create a new post (thread) or reply to an existing one. The posting can be made attractive by using specific font colour, size and inserting emoticons. 
To change text colour, click and drag your mouse to select the text and then click font colour.
You can insert a web address hyperlink. Select the text as above and click the URL tool.

You may also attach files including images.
There are lots of options, try them out. 
Please let me know if any of the features are not working.