For my project, the Arduino output is not enough so digging on the net and asking to a friend some help, I managed to build an amplifier to feed my 3 computer fans.
This circuit can be used as an amplifier to switch on and off a DC motor and to regulate its spinning speed with a PWM source generator. In my case the PWM generator would be the PIN 9, 10 and 11 from the Arduino board.
Read more: An amplifier for Arduino