When messages are posted on your thread, you can decide whether or not to mark a question as answered.
When you navigate to your thread, a prompt appears above your thread asking you whether or not you want to mark the question as 'answered'. Only do so if you believe that your question has been answered by one or more of the messages on the thread.
Once you mark your question as answered, the question appears in the thread list of the forum with symbol that indicates that it has been answered (). Note that this does not close the thread. Other participants can still submit messages. By marking the question as answered, you only inform other forum users that you, the creator of the thread, believe that your question has been answered. Other users can continue to discuss the thread.
You can also mark answers as 'Helpful' or 'Correct'. This gives other users an indication of the quality of the messages in question.
If the forum is moderated, the moderator can mark a thread as assumed answered ahead of time. If this happens, you can confirm the decision or declare that the thread has not actually been answered.
The control panel gives you an overview of all resolved and unresolved questions/threads. For more information, see Using the Control Panel for Forums.