When a voltage is applied to a conductor or semiconductor, electric current starts flowing.
In conductors, positively charged protons are held in a fixed position and the negatively charged electrons move from one place to another place by carrying the charge. Thus, electrons conduct electric current in conductors.
In semiconductors, both free electrons and holes carry charge from one place to another place. Thus, electrons and holes conduct electric current in semiconductors.
When voltage is applied, the electrons (negative charges) move from negative end of the battery to the positive end of the battery. So the electrons (negative charges) current direction is from negative to positive.
On the other hand, holes (positive charges) move from positive end of the battery to the negative end of the battery. So the holes (positive charges) current direction is from positive to negative.
The conventional current direction is from positive to negative (same as the current direction of positive charges).
The charge of a positively charged particle (hole) is equal to the charge of a negatively charged particle (free electron) but opposite in polarity.
A flow of negative charges in a circuit will produce the current same as the flow of positive charges produce. So it does not matter whether the current is flowing from positive to negative or negative to positive, the generated current will be same.