My previous idea of a flat tax (over here in Europe) referred only to a flat taxation of income. The "fairtax" proposal you link refers to a flat taxation of sa

My previous idea of a flat tax (over here in Europe) referred only to a flat taxation of income. The "fairtax" proposal you link refers to a flat taxation of sales; also there are payroll and income taxes in the US. What I don't understand: What's the difference between a flat taxation on sales vs income and, also, what's the difference between a payroll tax vs income tax?