Information regarding part-time jobs:

*Laws for Student Part-time jobs* (Dec, 2017)

As an international student, you are allowed to take up part-time employment along with your studies while in Germany. Here are a few things you need to keep in mind though.
You can work for a total of 120 full or 240 half days in a year as a student. This, however, might vary from high employment regions to low employment regions. Simply put, if your university is in a place which is in a city which has high unemployment rates, or requires more manpower, you might just get a work permit for more than 120 days.
Usually, as per university norms, a student would not be allowed to work for more than 20 hours in a week during term. Students, however, can take up full-time employment during vacations.
A work permit from the “Agentur für Arbeit” (Federal Employment Agency) and the foreigners’ authority is required. The permit would have details of the maximum limit of work a student can take up.
If you are enrolled in a preparatory course or a language course, the regulations are tighter. As such, you are allowed only to work during the lecture-free periods and only with explicit permission to do so from the foreign authority.
Taxation is another concern. A student earning less than 450 euros a month need not pay any taxes/ social security contribution. Also, if you work for less than 50 continuous days over a period of one year, you are exempt as well.
Working for more than 20 hours a week is generally not advised. Not only is it against most university rules, working more than this limit would require you to pay health insurance, unemployment as well as nursing care insurance.
Compliance with the Federal Laws is extremely important. If you are found to be flouting them, you can find yourself being expelled from the country. So, keep the checks in place, conform to the rules and have your permit in place.
When it comes to working within the University, though, the working hours and wages are completed differently. In fact, they are far better and you can work for long hours as well. Getting a job in the University, however, might not be as easy.