Restarting Nginx – what does this error message mean?

I followed the official DO tutorial in setting up Nginx server blocks and somehow always end up with an error message that is quite cryptic for me as a beginner. Going back every step I did before I checked for little typing errors, but no semicolons or other things seemed to be missing. Can someone give me a hint what this error message means?

sudo nginx -t
  nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
  nginx: configuration file /etc/nginx/nginx.conf test is successful

sudo systemctl restart nginx
  Job for nginx.service failed because the control process exited with error code.
  See "systemctl status nginx.service" and "journalctl -xe" for details.

systemctl status nginx.service
  nginx.service - A high performance web server and a reverse proxy server
     Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset: en
     Active: failed (Result: exit-code) since Fri 2018-12-28 10:42:09 UTC; 10s ago
       Docs: man:nginx(8)
    Process: 4686 ExecStart=/usr/sbin/nginx -g daemon on; master_process on; (code
    Process: 4676 ExecStartPre=/usr/sbin/nginx -t -q -g daemon on; master_process

Thanks a lot in advance for any help!