Here are the ways that poll taxes and literacy tests preventing groups of people from voting
Poll tax: Poll tax prevented the poor and even the middle class people from voting because, well, not everybody has the money to squander on voting. Only the rich people have extra income to pay poll taxes.
Literacy tests: Literacy tests were the big problem during that time, because even if a person is rich, if he couldn't read, he isn't able to vote. This meant that few people are able to read a couple of lines of words, which gives colored people a even harder obstacle to surpass to vote, as many were illiterate
hope this helps
