I've tried a lot of different ways to make a melody with my buzzer but certainly I can't. Im trying to make a "turning-on-computer" like sound, like a windows one or something like that. My teacher told me that each buzzers sounds different due to its smallness.
Could someone help me coding a nice short melody? Approx. 5 sec.
Spend some time with File > Examples > 02.Digital > ToneMelody and the associated tutorial:
https://www.arduino.cc/en/Tutorial/toneMelody
After that if you have specific questions come back here and we'll try to help you.
I won't, better copy someone elses
Generally we help people learn for free but if you won't make that effort you have to pay. How much money are you willing to pay for a melody code?
Actaully I paid nothing and found lots of free Arduino melodies in Youtube, you will have to find another way to earn your living. 
Do research, find answers. What a revolutionary concept!
I wasn't looking for your money but others on this forum are happy to pick up gigs. Arduino is a hobby for me. If I start getting paid for it the fun will be lost. I also don't consider writing code on demand for free to be fun, even though it usually would be much less work than helping people learn how to write their own.
Sorry if I was rude, I was desperate. 