Installation does not work!

I only get "Internal Server Error"...

https://learn.getgrav.org/troubleshooting/internal-server-error

Thanks, but that does not help me. I am on a shared hoster, I do not have access to the shell. Grav claims to be simple, but it is not at all...

Grav is really best with shell access (IMO). If you installed via FTP, then double check the warnings here. If you have no shell access, you're going to need some way of seeing detailed error messages. Check your server logs (through whatever facility your provider exposes) to see what the actual error is that's occurring. Otherwise it's impossible to provide more specific advice.