In any work of literature, the rising action comprises an event, or a series of minor events, that come together to move the action, the plot, forward.
In the story "A Jury of Her Peers", the event that sets off the story's dynamics occurs when the women, Ms. Hale and Mrs. Peters, start to find the so-called "trifles" that are actually evidence of the state of mind of Minnie Wright at the time of the commission of the murder of her husband.