Two people buy a car, a rich man and a poor man. Both buy a $1000 beater at 20% tax and pay $200 in tax. The system treated them both fairly and equally.
However, reality says the rich man will buy a $100,000 car...which means he will pay $20,000 in tax. They are still both being treated fairly and equally.
The Fair Tax stops caring about your income and only cares about your outgo. This means the illegals, the drug dealers, the prostitutes, etc., will all start paying taxes.
Basically, it is your standad consumption based tax with some changes to make it fair to those who are poor.