Many students work part-time to finance their studies and foreign students can do the same without having to get a work permit.
However, if you come from a non-EU country the amount of time you are allowed to work is limited to 90 days per year with 8 hour working days, or 180 half days per year. In some federal states, you are only allowed to work during vacation. Contrastingly those coming from within the EU have the same free access to the labour market as German students do.
Typical student jobs include working in a bar, office work, courier work, taxi driving (though you need a special permit for doing this), hostess work on fairs (well paid) and street cleaning in winter. Pay for student jobs is typically €6-10/hour. Vacancies are often promoted on newspaper websites, via student unions or the university.
As part of their studies, many German students do apprenticeships during their summer or winter holidays. These offer first-hand experience and direct contact with potential employers. People leaving university without ever having worked in the "real world" might find it hard to get a job.
Universities often help with organizing appropriate internships, especially during summer vacation.
There are magazines that focus on career issues for university students and young professionals, such as Junge Karriere. Its website has information on employment perspectives in different industries, tips and tricks for writing CVs, a job spider which searches through different job engines, an list of headhunters and information on career fairs - www.jungekarriere.com.
If you get a permanent job offer after university graduation, don't forget that you are not permitted to remain in Germany with a student visa. Official policy is that you must return to your home country before you can apply for a residency visa and work permit. However, if your employer wants you to start working quickly, this can be avoided by a lawyer making a petition on your behalf.