The rules for the creation and use of materials for universities are largely based on the terms and conditions set forth in Creative Commons CC BY-NC-SA 4.0. This means that the materials may be reproduced, further disseminated, and adapted, in whole or in part, in any format and media, subject to attribution (identification of the creator(s), the copyrights, and any modifications made), used for non-commercial purposes only, and disseminated under the same terms and conditions (ShareAlike). Further details can be found under the above link.
For details, see GTB Guideline (German).
Please also note that some of the attachments are not available in English language.