A QuestTrigger is used to trigger the QuestWindow to show. So it is responsible to give a quest to the player or to let the player complete the quest. The QuestTrigger is used together with a QuestCollection.
Trigger Type defines the player – npc interaction. In other word, whe the trigger should be used to complete a task, quest or to give a quest.
In the QuestCollection you set the quests that should be given to the player.