There is a good guide at the link below.  But the book is mainly about workers in a meat packing plant in Chicago and was designed to display the incredibly terrible conditions that were common to people who went to Chicago to work in the industry.  Though some things were appealing about the jobs, better wages, etc., there were also incredibly terrible things, injuries, deaths, horrific working conditions, etc.

By depicting the lives of ordinary people working in the industry, Sinclair created a powerful message that resonated throughout the country and led to significant reforms and changes in the way business was done.