Junior research groups pursue a research project in their own working group. The group is led by a successful postdoc and usually includes one or two doctoral students and, if necessary, student and research assistants or technical staff.
This group leadership can be an important step towards a professorship.
As a rule, you can do independent research for five or six years. You will be given budget responsibility, have a good infrastructure at your disposal and choose your own staff.
You conduct research, supervise doctoral theses and dissertations of students and give about two lectures per semester.
(Link: https://www.academics.de/ratgeber/nachwuchsgruppenleiter )