The 13th Amendment improved African American's way of life, by abolishing slavery.
The 14th Amendment changed the way people could become citizens. It allowed those born or naturalized in the U.S. to become citizens, which included the recently freed slaves. It also forbids states from denying anybody "life, liberty, or property, without the due process of law" or to "deny to any person within its jurisdiction the equal protection of the laws."
The 15th Amendment prohibits state or national government from denying anybody the rights to vote based on race, sex, religion, etc