quantization of charge means the total charge on the isolated body is always calculated by the formula
Q=ne
where n is no of charge and e is charge on electron which is 1.6×10 to the power -19

quantization of charge means that charge cannot take any arbitary values.

Quantization of charge means that charge cannot take any arbitrary values, but only values that are integral multiples of the fundamental charge (charge of proton/electron).

One quanta of charge is simply the charge on a single electron = 1.6 E-19 Coulombs

Materials have electrons bounded to atoms. Under normal conditions, some electrons gain energy and become free electrons which move randomly in all directions. When external voltage is given, these electrons starts moving in a particular direction . This is how electrons travel in a conductor.