Hi @Nino1983, let me see if I can help out here.
I have translated your question to English as this is an International forum, please post any replies in English and it will be easier for me and other users to assist you.
Safe mode is a troubleshooting mode that deactivates all apps downloaded from Play Store and is mostly used to detect whether an unwanted behaviour is caused by a downloaded app or not. To exit safe mode, simply reboot your phone as usual and make sure that the volume down-key is not pressed down during the boot sequence. If you want to read more about safe mode and how to use it, click here.
Let me know if that helped!
