I hope to finish the video the upcoming weekend.
@Aneroit: Here’s a screenshot of the dialouge system:
In this case the green NPC serves as a quest giver after you said the right things to him (accepting his request).
But quests can be given to the player by practically anything. That way NPCs can give the player smaller quests but you could also give them to the player at the beginning of the game or a certain level.