Answer:
There were several ways they did so.
Poll taxes
They introduced poll taxes which required that people who wanted to register to vote would pay a certain fee/ tax before they could register. As Black Americans had just been freed from slavery as well as being marginalised and disenfranchised, most of them could not afford to pay the taxes.
Literacy tests.
These states also enacted literacy tests that served to test the literacy level of a prospective voter. This went against black Americans as well because they had not been educated as enslaved people and even then were barely being provided with education. Many of them were therefore unable to pass the tests.
Grandfather clause
To ensure that some poor or illiterate whites could still vote, these states enacted a ''Grandfather clause'' which stated that the above laws did not apply to people whose grandfathers had voted at least once before slavery was abolished. As Black Americans could not vote at the time, none of them qualified.
White Primaries
While it was Unconstitutional to refuse Black Americans the right to vote for American offices, it wasn't when it came to party primaries where candidates were chosen. These white primaries only allowed white people to vote which meant that only white people would decide on candidates.
Violence and Intimidation
By engaging in violence against Black Americans, some groups hoped to intimidate Black Americans into being too afraid to vote. They even went so far as killing those who would resist.