District 12 is made up of two main parts. The Merchant area (or the "shops") and the Seam. The Merchant area is still poor, but compared to the Seam it is financially better. The wealthier District 12 citizens live in the Merchant area. The Seam is the poorest civilization in Panem. The coal miners live and work in the Seam. It is for the poorest people of District 12, or even the entire nation of Panem!
District 12 is a dirty, beat-down, poor District. It has no value to the Capitol and most of the residents of the District starve. I hope this helped.