Dear Younes,

I presume that you are asking about "Working or Operating Principle of DC Motor". The last link is a film of "DC Motor, How it works?"

Here are few attached links you will find them very useful:

http://pcbheaven.com/wikipages/How_DC_Motors_Work/

http://www.electrical4u.com/working-or-operating-principle-of-dc-motor/

http://www.solarbotics.net/starting/200111_dcmotor/200111_dcmotor2.html

https://www.youtube.com/watch?v=LAtPHANEfQo