How to start nginx via different port(other than 80)

You have to go to the /etc/nginx/sites-enabled/ and if this is the default configuration, then there should be a file by name: default.

Edit that file by defining your desired port; in the snippet below, we are serving the Nginx instance on port 81.

server {
    listen 81;
}

To start the server, run the command line below;

sudo service nginx start

You may now access your application on port 81 (for localhost, http://localhost:81).