The 15th Amendment was important because it gave African American men the right to vote. It was passed in 1870 and stated that the right to vote was guaranteed to any person no matter their race, color or "previous condition of servitude."
Although the Amendment passed in 1870, there were other ways of keeping black men from voting. The southern states disenfranchised African Americans, and literacy tests and poll taxes were enacted to keep African Americans away from the polls. It wasn't until 1965 and the passage of the Voting Rights Act that African Americans could truly vote. When the Amendment became ratified, United States troops were keeping peace in the South. Once they left, the white people in the area took over and would not allow any African American whose grandfathers were not citizens to vote without paying a fee that many of them did not have.
The 15th Amendment also gave African Americans the right to be elected to public office. Once they got elected, they helped to pass laws that allowed children of all colors to attend school, and people of different races to get married.
Before the amendment passed, African Americans were not considered citizens of the United States and non-citizens were not allowed to vote.