Here are some quotes and explanations from Chicago Poems by Sandburg:

Hog Butcher for the World,
Tool Maker, Stacker of Wheat,
Player with Railroads and the Nation's Freight Handler;
Stormy, husky, brawling,
City of the Big Shoulders

This is from the poem "Chicago," in which the poet describes the energy and power of the city of Chicago. Later in the poem, he also explains the city's pride and its "lifted head singing." He describes the city as "you," as if he is in dialogue with a person. The city is powerful yet has a sense of humanity.

I say good-by because I know they tap your wrists,
In the dark, in the silence, day by day,
And all the blood of you drop by drop,
And you are old before you are young.
You never come back.

This is from the poem "Mill-Doors," in which Sandburg describes the way in which the mill saps the life of those who work in it. "You," the person the narrator addresses, never comes back because the hard work of the mill forever ages and changes the worker. The mill takes the worker's energy away drop by drop.

PASSERS-BY,
Out of your many faces
Flash memories to me
Now at the day end
Away from the sidewalks
Where your shoe soles traveled
And your voices rose and blend
To form the city's afternoon roar
Hindering an old silence.

This is from "Passers-by," in which the poet writes about the hordes of people who pass by in the streets and the ways in which he later recalls them, their faces, and their messages. They blend together, forming a mass of humanity. Though the city of Chicago is immense, its people give it a sense of humanity.

It is the men and women, boys and girls so poured in and
out all day that give the building a soul of dreams
and thoughts and memories.

This is from "Skyscraper," a poem in which Sandburg personifies a great skyscraper in Chicago. The skyscraper is august and powerful, but it is also a symbol and a reflection of the people within it. Their dreams and hopes give the building humanity.