Official certificates and degrees are very important to find a job in Germany. You can graduate from university, but for certain professions it might be better to take vocational training with an apprenticeship (Ausbildung).
Vocational education is based on courses at one of Hamburg's 39 vocational schools in combination with an apprenticeship at a company or institution. The aim is to get both practical and theoretical knowledge. Typically, you visit school once or twice a week, sometimes also for a couple of weeks in a row every few months. The other days, the apprenticeship takes place in a company, where you're instructed by your supervisors. It's also possible to spend most of the time in school, in combination with several internships to gain practical experience. For some professions, it's required that you have finished your A-levels in order to enroll. It usually takes three years to finish vocational training, but depending on the profession you're training for, the type of degree you’ll get and your final grades, your education may take shorter or longer.
For further information in English, visit the website of Hamburg's Chamber of Commerce. Or take a look at this video by The Chamber of Commerce. For information about visa and work permits, visit the website of the German Federal Foreign Office.