Is is possible to modulate voltage

[mikey00409]

I am doing a project for school to control a DC motor using an Arduino Uno card. I want to know if it is possible to modulate the voltage output on any of the pins. What I would like to try to do is connect a dial input from the front panel that would allow me to increase and decrease the voltage to the motor. When testing the Arduino card I found that I get 5 volts out however my motor is rated at 1.5-3 volts. So I would like to be able to reduce the amount of voltage and be able to adjust it from the front panel. Can anyone help me do this?