Students who are nationals of EU or EEA countries do not require any special permission to start working in Germany. There is only one rule you need to mind: in case you work more than 20 hours a week, health insurance contributions are applicable.
Non-EU/Non-EEA students require a valid German visa or a German residence permit to engage in gainful employment in Germany. You are allowed to work for a total of 140 full days or 280 half days per calendar year (January to December).
Any mandatory or compulsory internships (Pflichtpraktikum) that are recognized as a part of your study programme are permitted and do not count toward the 140 full-day/280 half-day annual quota.
During the lecture period, a maximum of 20 hours per calendar week is permitted. During the lecture-free period (e.g. a summer break), it is permitted to work more than 20 hours per calendar week.
Self-employment and freelancing could only be allowed if exclusively stated on the supplementary sheet (Zusatzblatt) of your visa or residence permit issued by the German immigration authorities.
Should you have any case specific questions, then please feel free to contact us at visasupport.berlin@escp.eu.