To control the motor, i will be using an H-bridge with a DPDT relay like you can see on this schematic below.
If you want more details, look on this page :http://oomlout.com/a/products/ardx/circ-11/
This circuit allows the motor to run in forward and reverse weither we set the Arduino pin HIGH or LOW.
The problem with this circuit is that it doesn't allow us to stop the motor *gasp*
In order to stop the motor when we want it, we will need to unplug one of the motor wires, and plug it into another bit of circuit with a kind of Switch hooked up to another Arduino pin.
I did that by inserting another relay in my circuit ( an SPST or SPDT relay will do fine ), controlled by another transistor ( hooked up to another Arduino pin set on OUTPUT )
I tested the circuit with two LEDs :