Hello,
The discussion boards are very straightforward. Basically, a question/topic is posed and you are required to provide an answer in at least 250 words, citing your references. I like to carve out a chunk of time where I can think about what is being asked and put together my response before posting to the site. The library link has detailed information about how to cite references so I would strongly suggest reading through that before posting so you have the correct format. As far as the discussion topics go, you can look into the discussion board beforehand if you want an indication of how it looks, but the topics do change (I think on a daily basis but I'm not sure of the actual timeframe).
Once you actually post your own response, other people's responses are available to read and you are able to comment on those if you wish.
Hope this helps - don't worry about answering, I'm sure you will do fine. Focus on one step/assignment at a time and give it your best. Then celebrate your smaller successes - they all add up