How does resistor exactly reduce current flow in circuit?
For the current to flow, the current must flow at each point of the loop of the circuit. some electrons will flow in the wire on the positive terminal, others in the wire of the negative terminal and others in the resistor. the important thing is that the number of electrons passing through any section of the circuit is identical. so that the loss of power and the voltage drop will be created by the electrons of the resistance.
Another way to see this is that the electrons between the resistor and the positive terminal can not all be drawn into the terminal. the number of electrons in the wire must remain the same. likewise every electron that flows from the wire into the positive terminal must be replaced by another electron that flows from the resistance in the wire. and the same thing happens to the other thread. the electron that has reconstructed the first wire must be replaced by another electron of the second wire in the resistor. and now, the missing electron of the 2nd wire must be replaced by an electron of the
(all that assumes ideal wires with zero resistance)
I think you wonder why all the electrons of the resistance wire at the terminal positive does not flow because there is little resistance between the load and the positive terminal. If this is your question, then the is due to the voltage drop across the resistor. there is no potential difference between the positive and the positive side of the resistor. in this circuit, the applied voltage will be equal to the voltage drop across the resistor and so there will be no potential difference between the positive terminal and the resistor.
you can also consider this electrical circuit (and most others) as a water or plumbing circuit. the resistance in the plumbing circuit would be a pipe of smaller diameter than the rest of the circuit. water will flow from high pressure to low pressure. the flow of water from the source through the resistor is limited by the size of the pipe in the resistance and the water pressure potential difference. the water flow of the drain resistance is limited by the amount of water passing through the resistance, which was limited by the size of the pipe in the resistance and the difference in water pressure.