Short answers, pulled from the story.
The Fifteenth Amendment was ratified on the 3rd of February, 1870. Secretary of State Hamilton Fish certified it as part of the Constitution on the 30th of March, 1870. It was the third and final of the Reconstruction Amendments.
The Fifteenth Amendment prohibits the federal government or any state from denying or abridging a citizen's right to vote on account of race, color, or previous condition of servitude. It does not, in the Court's interpretation, itself confer the right of suffrage; it prohibits racial discrimination in the exercise of that right.
Thomas Mundy Peterson cast his ballot on the 31st of March, 1870, in a Perth Amboy, New Jersey referendum on a revised city charter, making him the first black person known to vote after the amendment's adoption.
The Fifteenth Amendment prohibited race-based voting restrictions but said nothing about sex-based restrictions. Leaders of the National Woman Suffrage Association, including Susan B. Anthony and Elizabeth Cady Stanton, opposed ratification on those grounds. The dispute split the American Equal Rights Association into two rival organizations that remained divided until the 1890s.
From 1890 to 1910, Southern states enacted poll taxes, literacy tests, and grandfather clauses that exempted white voters while effectively barring most black men from registering. White-male-only Democratic primaries and violent intimidation by groups including the Ku Klux Klan reinforced these legal barriers. By 1940 only five percent of Southern black men were registered to vote.
In Shelby County v. Holder in 2013, the Supreme Court ruled that the coverage formula in Section 4(b) of the Voting Rights Act of 1965 was no longer constitutional. The ruling disabled the preclearance mechanism that had required jurisdictions with histories of discrimination to seek federal approval before changing voting laws. The preclearance provision itself was not struck down but remains inoperable without a new coverage formula from Congress.