The narrator essentially learns almost everything about the elusive Ethan Frome through other people in the town. He is intensely curious about the unique man, and so asks a lot of questions. He gets bits and pieces from several different townspeople--the grocer, Mrs. Ned Hale (who he is boarding with while he is in town), and Harmon Gow (who drives the narrator places in his cart). From each person he gets a different little bit of information: from the grocer, he learns that Ethan had a "smash-up" about 24 years ago that crippled him, from Gow he learns about Ethan's sickly parents and Zenobia, his sickly wife, and from Mrs. Hale he learns a few more details about Mattie, relating to why and how she came to stay at the Frome household. So, he starts to piece together the foundation of Ethan's story through the other characters.
It isn't until the narrator visits Frome's household and sees both Zeena and Mattie in the house together that he really feels like he understands Ethan Frome. It is at this point that the narrator has a "flashback," and Wharton goes back and tells the beginning of the story that we have missed, filling in all of the details that the townspeople haven't told him already. I hope that those thoughts helped a bit; good luck!
In the book "Ethan Frome" the narrator learns from Mrs. Hale that Zeena, Ethan's wife, had been sickly. Mattie Silver, Zeena’s cousin, had been Mrs. Hale's good friend after she had moved in with the Fromes. She tells how Ethan and Mattie had gone on the sleigh ride and crashed. Mattie screamed in agony when they brought her inside. Zeena had jumped right up and went to check on Ethan as if she had never been sick. Zeena had Mattie moved to her own home and was now caring for the three of them. Mrs. Hale made Zeena sound like a saint. Mattie was confined along with Ethan and Zeena indoors in the winter. She had no ability to move about without them moving her. She had become bitter thorough the years and would argue with Zeena. Ethan was stuck in the middle with a face of such misery that Mrs. Hale stopped trying to visit.
Her last statement to the narrator was that Mattie would have been better off dead, because it was as if the three were already dead.
"I don't see's there's much difference between the Fromes up at the farm and the Fromes down in the graveyard; 'cept that down there they're all quiet, and the women have got to hold their tongues."(Chapter 9)