Hello Derar Rashed,
what students really should know abot paying taxes is explained by monster.de: https://goo.gl/shom9H
The informations are detailed and slightly different to what has been in a generalised way said in the first given answer. The Information language is German, but for you are a student in Germany, I hope you can understand the article without any trouble.
By the way: To answer your question completely: In case you should have to do your taxes contact your local finance office for special formulas. You can do your return of tax online too.