What are the narrative elements in Robert Frost's "Out, Out" and how do they convey the poem's main theme?

The poem is indeed a narrative poem.  It tells the story of a young man who has a fatal buzz-saw accident.  As he is cutting wood, his sister rings the bell for supper, and the saw slips slicing the boy's arm.  The arm is amputed, but the boy dies.  This sad poem is delivered in a conversational tone.  The narrator of the story speaks haltingly as if he is groping for words.  Like a story, the poem has a setting--an ironically beautiful setting in the mountains of Vermont--on a day that seems normal and peaceful.  The buzz-saw becomes the antagonist with its ominous sounds "buzz and rattle," and leaping up to meet the boy's hand, as if "it knew what supper meant."  We have minor characters as well:  the sister who calls for supper--also seemingly a child doing an adult's work, just as the boy.  We have the doctor, who takes fright as the boy's pulse diminishes.  And we have the rest of the family that turn to their affairs after the boy's death because life goes on.

The conflict perhaps is man versus machine.  But most likely it is more than that.  Frost shows us how quickly an ordinary day can turn to tragedy.  He creates pathos for this young boy who without his hand sees his life spoiled, and loses the will to live.  Life as described in this poem is hard.  Farm workers cannot take time to grieve a loss; they must continue on with their jobs.

How do narrative elements in "Out, Out - " convey the poem's main theme?

The main theme of this poem is the fragility of life and the meaning of death, and this is conveyed through the narrative style of the poem.  It reads like a story and has many short story elements.  There is a main character:  a young teen who is working on the farm "a boy doing a man's work."  There is a setting:  a beautiful rural location with the mountains of Vermont in the background.  There is a situation:  the boy has been working and is almost done for the day when he is called to supper by his sister.  At that moment, he loses control of the chainsaw, and in a shocking moment, his hand is cut off.  His first reaction is an odd laugh, but he quickly realizes the severity of the situation.  He puts his arm up to help stop the flow of blood "life" as it is identified with a metonomy in the poem.  He begs his sister to not let the doctor cut off his hand -- a childish reaction -- especially in light of the fact that hand is already gone.  The fragility of life is shown in the fact that the boys dies right there in the yard as a result of this accident.  He is young and had his whole life ahead of him, but this freak accident ended it all in an instant.  The theme of the meaning of death is revealed in the final two lines.  These lines come as a shock to the reader -- perhaps more of a shock than the death itself because they state that everyone around the boy just returns "to their affairs" because there is "nothing more to grow on there."  The boy is dead and nothing is going to change that fact, but there are things that still need to be done for the day to day existence at this place.  The people there may have been sad, but that is never stated.  What the poem ends with is the oddly calm acceptance of the death.  The pace of the story builds the suspence from the foreshadowing of the menacing sound of the saw as it "snarled and rattled" in line one, through the quick death of the boy, but we are left unprepared for the conslusion, and yet, if the reader recognizes the allusion of the title from its source in Macbeth we can better understand Frost's point.  In that play, the main character, Macbeth, states that life is like a brief candle.  The exact quote is "Out, out  brief candle."  The candle, like the life of the boy, is fragile and the death of the candle and the boy is inevitable and permanent, which is what Frost is conveying in this narrative poem.