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There are different types of driver's licences in Germany that are labelled with different letters. In order to drive a truck (Lkw) you either need class C, CE, C1 or CE1.
Here you find an overview of the different types (classes) and what type of trucks you are allowed to drive with them:
For all those driver's licences you first need a regular driver's licence (class B).
Usually, you'd have to pay for the regular driver's licence yourself, but there are exceptions: You can get a grant by Jobcenter or Agentur für Arbeit if you need the licence for a job. You need a document by your employer that proves that.
If you want to work as a truck driver, you need to do a so-called "Ausbildung zum Berufskraftfahrer" (apprenticeship to become a professional truck driver). Only having the truck driver's licence doesn't allow you to work with it. You can apply for a grant by Agentur für Arbeit for this apprenticeship as well.