Looking for help calculating needed resistor in circuit

Total newbie here, learning to interpret specifications...

I am putting a motor into a circuit and trying to figure out what resistor I need to use based on the motor's specs. I have it connected to the 5V pin.

Here are the motor's specs:

Voltage range: 1.5-3VDC Current: 0.18-0.25A at no load 0.70A +-15% at max efficiency

I have been reading all I can on Ohm's law, but I just can't understand how to use the known info I have (the above specs, plus the 5V supply) to end up with a resistance value that makes any sense to me.

You need a transistor to handle the max current flow motor, the arduino can drive the transistor on/off.
This picture shows how to connect all the dots, so to speak.