The party window is only active once you have joined a party or other players have joined your party. This will display the HP and MP for all members in your party. This window is particularly helpful in Clan Wars or Siege Situations.
Most functions related to the party features are located in the Party Action section of the Action tab and they can be used to form parties with other players.Once you form a party, you can chat with your party members exclusively through the party chat window. Click on the Party tab in the chat window, or enter @ in the chat window and then type your message.