Finally there is a light!
I do not remember the steps exactly, but mainly if someone having the same problem (running CentOS 6) you need to:

nano /etc/nginx/conf.d/virtual.conf

add the code what was already mentioned many time:
https://github.com/designcreateplay/NodeBB/wiki/Configuring-nginx-as-a-proxy-to-NodeBB
So my problem was that I was not able to figure out the right files to edit! (when you guide people, you might always remind the path or mention exact file need to be edited - what is obvious for you, might be obscure for others)
Now the forum works fine, but there is a new problem:
I want to run nodebb only at http://forum.caffeh.com (as sub-folder or sub-domain) but I can see it is same running at the root (caffeh.com ) and at the server IP 37.59.29.104
My virtual.conf file:

server {
listen 80;

server_name forum.caffeh.com;

location / {
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Host $http_host;
    proxy_set_header X-NginX-Proxy true;

    proxy_pass http://127.0.0.1:4567/;
    proxy_redirect off;

}

}

Community

xpcontact