There are courses where you can get your grades via Campus Management, and there are courses where you have to collect a course certificate (in colloquial German: "Schein") from the course instructor.
You will find that information for each course in the course descriptions that are available on the website
http://www.jura.fu-berlin.de/en/international/studierendenaustausch/incomings/kurse/index.html (at the bottom of each course description)
Please check Campus Management regularly. For all other courses, please ask your course instructors when and where you can get your course certificate. Course certificates are usually distributed by the professors' secretaries during their office hours.