My educational level in mathematics is falling down at the first year in the university and i am studying engineering ...and i don't know what i do !

Need more info: There are many reasons for your concern. This ranges from emotional problems like anxiety, depression and any drugs you might be using. Then there is the question; do you really want to study engineering?? I would suggest that you should first talk with your professor and then seek some advice from a psychologist.

Work harder: More time studying and less time partying. Usually remedial help available from grad students, proctors etc. Cut out beer, partying and funny cigarettes.