You posted a message, so that is part of the battle.
If you want to start a new message thread, you'll want to decide which section to place it in, so you should go to the main forum list which should look like this.
Once there, you pick the section such as Carnival Cruise Lines by clicking on it in the left column. That will give you this. Click on the orange box at the top and you'll get the message window where you can start your new thread.