Jeff,
There are three ways to reply to an open thread. Dave mentioned the quick reply. To reply with a quote, hit the little blue "reply" box at the bottom right of the post you want to reply to. At the bottom left of the thread, there is a "post reply" box that will post a reply without a quote. Both of these replies add a message to the original thread. Open replies are fine most of the time. We all enjoy reading them.
To reply privately, you can click on the person's screen name to send them an email or PM (private message). I only use these two when I feel the world does not need to "hear" the conversation.
Keith
2008 NWR Bash Crappie Champion
2010 NWR Bash Yellow Perch Champion
2010 Buggs Bash Smallest Crappie Award