World Chat is the in-game chat system available to players where they can ask questions, discuss, and have conversations with one another no matter where they are in the game. There are categories within the World Chat that you can also join including All, Nationality, Adventurer, Merchant, Military Man, and more. School Chat is for those who are new players.
In order to access the World Chat, click the button on the top right of your game which has two people with speech bubbles. Once clicked, select "World Chat Settings". Choose the chat room you want to join.