This can all be learned in the first chapter.
The town is the fictional Maycomb, Alabama (loosely based on Moblie, AL). It was "a tired old town" then, during the Great Depression. The events of this novel seem to unfold between 1932 and 1935. The town had just been told that it had "nothing to fear but fear itself." These words of FDR verify the time period.
The setting of red slop streets and a sagging courthouse in the middle of the town square help portray the destitution of the times. The description on page 5 of ladies ambling across the square, of the sweat and sweet talcum give us a vivid understanding of the hot and dreary times. This is important because the subject matter of the main part of the novel is both hot and dreary.
Being set in the Depression also demonstrates the desperation people may have had. I think the Ewell family that goes after Tom Robinson does so because the see the opportunity to take advantage of someone less than them.
The setting offers opportunity for a racial conflict to brew to complicate matters being set in the south. Being a bible belt area, this also gave reason for moral complications to arise which helped the children look at the perceptions, the example of their father, the question of what is right and wrong. Rising action is just that, complications.