Create a directory, /etc/nginx/ssl:

$ sudo mkdir /etc/nginx/ssl

Generate a new certificate using the following command:

$ sudo openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout /etc/nginx/ssl/nginx.key -out /etc/nginx/ssl/nginx.crt

At this point you will be asked to provide some information about the new certificate, as shown in the following diagram:

Open the learning-phalcon.localhost configuration file (/etc/nginx/sites-available/learning-phalcon.localhost) and enable SSL:

server {
  listen 80;
  listen 443 ssl;

  ssl_certificate /etc/nginx/ssl/nginx.crt;
  ssl_certificate_key /etc/nginx/ssl/nginx.key;

  #....rest of the code
}

Then reload the Nginx configuration:

$ sudo service nginx reload