How was the literacy test used to suppress the vote of african americans?

They asked if their grandfather was a citizen on the date of before the day that african americans were legal citizens so they couldn't vote.

from my own personal expirence food stamps has alot this makes it eaiser so we can affod bills and so we can life a better lifestyle not needing to worry about paying actual money to buy food since most people spend 100-300 dollars a month on food so this alot so we can afford other bills and other stuff we need

is it multiple choice