You can find information on all fees and contributions that must be paid in advance of the school year here.
If you are about to embark on your Master's program and currently in the process of enrolling, you will be granted a leave-of-absence for the duration of your first year. For this you must submit a formal request in your application. Should this be case, you will not be paying any fees. Semester fees for the Freie Universität will only have to be paid once you enter the final year of your studies