What was the impact of the Civil War upon freed slaves once slavery ended, and what were the various opportunities opened to them, and what were the struggles they faced?

With the conclusion of the Civil War many of the governmental and societal policies in place continued with little change. The South was forced to give up slavery, but they tried to create new forms of societal control in an attempt to maintain societal control. One of the ways that they did this was through the implementation of the sharecropping system, in which, former slaves often agreed to work for their former owners to maintain their crops in exchange for a portion of the profits. This system was heavily racialized and the former slaves were not considered equal to white southerners so they could not bargain for better terms.
The Federal government attempted to intercede in the affairs of the freedmen through the Freedmen's Bureau, but were largely unable to properly respond to the conflict that arose between plantation owners and sharecroppers.
Also the former slaves dealt with health issues that were left unchecked in the new system which led to widespread disease.
Lynchings were also common during this time period which coincided with the rise of the first iteration of the Ku Klux Klan.
All in all, it was not a positive time in the history of American race relations. But Reconstruction (1865-1877) did allow for some former slaves and free blacks to hold a position in Southern governments, but following the "redemption" of the South (when control went back to white southerners in 1877) it became increasingly hard for blacks to have a role in government.

While the Civil War, and more specifically the 13th Amendment, ended legalized slavery in the United States and gave approximately 4 million former slaves their freedom, it did not mean that the lot of African Americans improved as much as many had hoped.
Freedom did bring many new opportunities to them. African Americans were now permitted to relocate, maintain families without fear of separation, run businesses, vote, participate in politics, own property, learn to read and write, and organize their own churches. Thus, former slaves were able to improve the conditions of their lives in ways that were completely unavailable to them before abolition. In fact, hundreds of African American men served in elected offices in the first decade after the Civil War. When safe-guarded by the federal army, former slaves participated in elections and other civic arenas at rates far surpassing their white neighbors.
However, just because former slaves were entitled to the opportunities listed above, they did not necessarily have access to them. Many white Southerners went to great lengths to keep African Americans subjugated as much as possible. Groups of white supremacists, most notably the Ku Klux Klan, did all that they could to intimidate and terrorize African American communities and anyone who supported them.
Things got worse after Reconstruction ended in 1877. With the withdrawal of federal troops, Southern governments were essentially free to impose laws, known as Black Codes, with the purpose of recreating the conditions of slavery as much as possible. New legal methods were introduced to limit African American involvement in the public sphere. Lynchings and other attacks became commonplace. African Americans became increasingly barred from operating business, owning property, and even gathering openly together. As a result, most former slaves remained impoverished.
http://nationalhumanitiescenter.org/tserve/freedom/1865-1917/essays/reconstruction.htm