Certain people in the game are considered NPC's and are not controlled by humans, but rather by the game system to react upon clicking on them. Their names show up green. Some only provide dialogue once you reach a certain part of the game. These guys give you quests, rewards, background of the area, and there are also Profession trainers, which are required to give you your profession skills. Every NPC is vital to the game and here is where you can learn about each one.