Final answer:
The rising action introduces the conflict or obstacle the main character faces.
Step-by-step explanation:
The part of a plot structure that introduces the conflict or obstacle the main character faces is the Rising Action. The rising action is comprised of a series of events that build up to the climax of the story. It introduces us to secondary conflicts and creates tension in the story. You can think of the rising action as the series of events that make the climax of the story possible.