What is the rising action in Susan Glaspell's play Trifles?

As others have said, the rising action occurs as Mrs. Hale and Mrs. Peters explore the kitchen area of the house with the observant female eyes of fellow rural housewives who grow, because of what they see, to have increasingly more empathy for Mrs. Wright. As the action rises, the two women imagine how lonely life must have been for the isolated Minnie Wright. Mrs. Hale remembers how vivacious Minnie once was and now regrets not having visited her more often to check up on how she was doing.

Mrs. Peters has a harder time empathizing, as she is a newcomer who never knew Minnie, but as the evidence unfolds, she is able to find more and more parallels between Minnie's life of isolation and loss and her own. While the men dismiss Minnie as a poor housewife—and miss the evidence that Minnie killed her husband—the two women realize that the Minnie was a careful housewife whose now somewhat-messy kitchen is an indication that she snapped.

As others have noted, the climatic point comes when the women discover the dead canary tenderly wrapped up—its neck wrung—and realize what pushed Minnie over the edge.

The plot of any piece of literature consists of the exposition, rising action, climax, falling action, and denouement. The exposition offers background information and an introduction to the characters and conflicts. The rising action is the complication of the events, where the conflicts become more involved. The climax is the most intense moment of the story, and the falling action is what happens after the climax. Denouement ties up any loose ends and clarifies any events.

The climax of this story is when the two women find the dead bird and realize that John Wright had broken its neck, taking away from Minnie the only joy she had in her sad life. The exposition starts at the beginning of the play, giving us the background of how John Wright's body was discovered and how they found Minnie sitting in her rocking chair. The rising action begins when the men go to look for "important" clues upstairs, leaving the two women in the kitchen.

The rising action is what leads to the climax. In this play, Mrs. Hale and Mrs. Peters use inductive reasoning to discover that Mrs. Wright has killed her husband. It is important to note that this is the dramatic irony of the play: the fact that the women solve the crime rather than the male attorney and the sheriff. Simply put, Hale's recounting of his story is the exposition. The rising action takes place as Mrs. Hale and Mrs. Peters do their detective work. The climax is their epiphany (along with the audience) that Mrs. Wright killed her husband and was driven to it.

Within the rising action, we get the character development and we learn how men treat women. We learn that the Sheriff and the County Attorney are oblivious to the significant evidence. We learn that the ladies' concern with "trifles" is what leads to the truth. This is one of the angles that illustrates misogyny in the play itself and as a mirror to society. Just as the ironically named Mr. Wright ignored his wife's needs, the Sheriff and Attorney ignore the significant evidence and anything the women have to say. (Another name for the play could be "Men Ignoring Women.") When the Sheriff mocks the ladies for wondering about Mrs. Wright's quilt, Mrs. Hale says,

I don't know as there's anything so strange, our takin' up our time with little things while we're waiting for them to get the evidence. I don't see as it's anything to laugh about.

She is stating the dramatic irony here. So, the audience also learns that the little things and trifles matter—it's the little details that help the ladies solve the crime and the little things that make life worth living (being in the choir, having a social life).

Exposition is revealed when Hale describes how he looked in on the Wrights to ask about a phone.  The first complication, which is the signal for the rising action, comes when the audience hears him ask why he can’t see John, and Mrs. Wright answers “because he’s dead” (Although this is told in retrospect, which makes it exposition, the telling to the sheriff is the complication.)

The action rises throughout the play steadily (this is virtually always the case in a short, one-act play) but we could say that the next “beat” begins when the men go upstairs. The turning point is the discovery of the bird wrapped in a cloth.  And the climax of the dramatic structure and tension occurs when the bird is intentionally concealed from the sheriff.

These technical terms to describe the parts of dramatic action are more suited to the “well-made” play as built and dissected by Eugene Scribe in the 19th century; “Trifles” is not only shorter, but is also a product of the emerging modern play movement, such as the naturalistic plays of Eugene O’Neill, and, in Europe, Ibsen, Chekhov, etc.

What is the denouement of the play Trifles'?

At the play's end, after the county attorney and sheriff have continued making demeaning remarks about women, the sheriff asks the attorney if he needs to check what Mrs. Peters is taking from the crime scene, and the attorney flippantly replies that it cannot be anything dangerous or significant. When the men leave the room, Mrs. Peters and Mrs. Hale make eye contact and silently agree that they will smuggle out the evidence of Minnie's dead bird (the motive for Minnie's murdering her husband). Glaspell writes in her stage directions that

"Mrs. Hale snatches the box [containing the dead bird] and puts it in the pocket of her big coat"

just before the men reenter the room. The attorney makes another joke about the trifles with which women concern themselves--such as quilting, and Mrs. Hale tells the attorney that it's not "quilting"; it's knotting (her subtle reference to Minnie's strangling her husband with a rope).

The denouement is significant because the women get the upper hand over the chauvinist law enforcement officials and decide to defy traditional gender roles by protecting Minnie Wright.

What happens after the resolution in Susan Glaspell's play Trifles?

Once Mrs. Peters and Mrs. Hale discover the bird with a broken neck, lovingly wrapped in silk and hidden in Mrs. Wright's sewing box, they know what has happened.  They realize that in a fit of rage, Mr. Wright must have killed his wife's beloved bird as the final crushing blow to her spirit. 

The women decide to hide the bird from their husbands, claiming that the cat must have killed it, because they realize the bird will be the evidence the men have been looking for to blame Mrs. Wright for her husband's murder.  Without saying it, there is an unspoken agreement and understanding for Mrs. Wright and her actions against her husband.