The setting of The Jungle is Chicago in the late nineteenth and very early twentieth century in a place known as "back of the yards." It is near the slaughterhouses where many of the immigrants work.
All of the elements mentioned—immigration, working conditions, living conditions, and sanitation—work together to make life a misery for the innocent Lithuanian characters who end up in this environment. They immigrate to the United States yearning to build a better life, but they are completely unprepared for what they encounter. They come from a small village in the woods and can barely conceive that they are now living in a smelly, crowded, polluted city. When they arrive at their new home:
They were left standing upon the corner, staring [at] a vista: half a dozen chimneys, tall as the tallest of buildings, touching the very sky—and leaping from them half a dozen columns of smoke, thick, oily, and black as night.
It is also noisy because of the factories.
If anything, working conditions are even worse for the men laboring in the slaughterhouses.
Being immigrants makes the Lithuanians targets for being cheated. From the start, unscrupulous people lie in wait for newcomers like them. They are cheated of much of their money in New York City. They dream of home ownership in Chicago, but when they buy a home, they don't understand the terms of the contract, which is constructed so they won't be able to afford the house over time. In addition, the house itself is shoddily constructed.
Sinclair's point is that capitalism grinds up and destroys innocent, hardworking people: it is a system, he argues, that needs to change.