What does the Fifteenth Amendment prevent states from doing?

The Fifteenth Amendment (Amendment XV) to the United States Constitution prohibits the federal government and each state from denying a citizen the right to vote based on that citizen's "race, color, or previous condition of servitude".

Answer: The 15th amendment prevents the government from not allowing one to vote because of race, gender, age etc. (in other words prevents discrimination and gives everyone voting rights)