Living cost in Germany is affordable however International students often need extra money which they can earn by having opportunity to work in their spare time while studying in Germany. 20 hours per week is a limit to work in one semester. If you want to work more than the allowed hours, you have to take permission from the local employment agency & the foreigner’s registration office. But during the semester break you can work without restriction. International students may also complete internship or engage in self-employed activities while at university. However, any self-employed activity requires the approval of the competent foreigner’s authority. The authority will consider, among other things, whether the work is likely to hinder or delay the student in the pursuit of their academic goals or not. 

More importantly, the international students can switch to vocational training if they find their academic study program has less practical approach. For that, the residence permit will need to be amended as the permit for vocational education & training assessment is done by the Federal Employment Agency.

Lastly, you can search for the part-time jobs at; University Bulletin Board, University Career Centers & Online Job Portals. Asking from friends & fellow students is also not a bad idea. You may get more helpful leads. You can apply for German PR after the completion of five years of residence in Germany, also called German settlement permit. After completing the graduation, one can work for 2 years on work permit but your job should match with your academic qualification obtained in Germany.