How does the firstchapter help you tounderstand the important themes and issues that will be approved later in the novel Focus on Simon finch
The first chapter of To Kill a Mockingbird prefaces many of the concepts and narrative strands to be explored later in the novel. It begins with a reference to one of the culminating events of the novel (Jem's arm being broken - it is appropriate for a child's version of the events to emphasise the broken arm part of the story rather than the attack by Ewell or the rescue by Radley), introduces the central family (the Finches), the geographic and social context of the story (quiet, hot little town in southern USA dominated by whites (but in which at least one, Boo Radley, is marginalised) in which African Americans are servants/employed workers).
You list the concept "focus on Simon Finch." Finch is the English ancestor of Jem and Scout who came to the US and as a wealthy man, established a plantation (complete with slaves) at Finch's Landing, about 20 miles from Maycomb. Finch's descendents continued the plantation, but the novel claims the family lost its wealth at the time of the Civil War. At the time of the events presented in the novel, only Atticus Finch's sister and her husband live at Finch's Landing.
Does this prefigure issues and themes in the novel? Only in a contextual way. The Finch family had money once and certainly Atticus Finch occupies a privileged position in Maycomb society. Part of this would be because of his education, but part would also be because his family has been in the area for a long time (it is my experience that such things are esteemed in rural communitites). What I'm suggesting here is that the Simon Finch story gives the reader a sense of Scout's family's place in this society - near the top.
The story also explains the presence of and low social status of African Americans in the town - that is, their ancestors were slaves. If you generalise the reference to the economic disruption of the Civil War for the Finch family to the rest of the county, that may also help account for some of the lethargy in the town, but I wouldn't push this too far - in historical terms, the Great Depression was probably more of a factor.