i dont understand y i should use a mosfet
please enlighten me
You don't have to
(although I did leave a a huge clue why you might want to)
I would suggest some reading... DC42's posts are a good start,and re-reading the article you posted (it tells you what the diode is for!) and find some data sheets on your motor, your transistor and then maybe also compare your requirements against a mosfet and see what conclusions you come to.
Draw an H=Bridge and see if you can understand how it works (think of the transistors as switches). Hint - nothing to do with high currents as suggested above. patduino suggested reading about transistors as switches - great idea (although you didn't seem to think so)
The exercise will hold you in good stead for your next project. Asking questions is a good way to learn, but doing it off you own back with a few pointers to get you going is so much more rewarding than expecting someone to do it for you! It really is worth the time and effort.
Lets hope your next post is a video of you controlling your motor!