A new conversation will be at the top of the conversation list.  Additionally, to the far right of the message, the 1 Messages (1) tally is displayed to let you know that you have one unread message.  The date the message was sent is also displayed to the far right.

A new conversation will be highlighted in gray to indicate that the message has not been read.  To read the message, simply double-click on it or click on it, then select Open Conversation.

To reply to a conversation:

1. Type the message in the Reply box.
2. Click the Send button to send your message.