How would you explicate the opening paragraph?

The opening paragraph of "Why I Live at the P.O." explains much of the background of the story and hints about the problems that its main characters encounter throughout the rest of the text. The narrator of the story is never given a name other than "Sister." In the first paragraph, the reader learns that things were going well with Sister and her family before Stella-Rondo (the narrator's younger sister) came to visit. However, once Stella-Rondo arrives, Sister says that her family relationships begin to deteriorate.
Stella-Rondo has recently separated from her husband Mr. Whitaker and returned home with an "adopted" child. Sister was the first person to show interest in Mr. Whitaker, and the two of them dated until Stella-Rondo broke up the relationship and married Mr. Whitaker herself. Stella-Rondo made up lies about Sister that ended her relationship with Mr. Whitaker.
As the text progresses, the reader learns that this family strife is common throughout the rest of their lives. All of the family members deny their faults and they are often bickering. Eventually the situation in the story is bad enough that the narrator moves out of the house and starts living at her place of work. The narrator now lives at the post office, which is the reason for the title of the story.