I'm also new to nginx, Here is my solution that is similar with Mohammad AbuShady's answer :

delete sites-enabled/default
create the whatever.conf in /etc/nginx/conf.d/

The reason is:
sites-enabled/default has defined a server
that is listening on 80 rooting with /var/www/html
server {
  listen 80 default_server;
  listen [::]:80 default_server;

  root /var/www/html;
  location / {
        # First attempt to serve request as file, then
        # as directory, then fall back to displaying a 404.
        try_files $uri $uri/ =404;
    }
}

the nginx.conf file includes other conf files
include /etc/nginx/conf.d/*.conf;
include /etc/nginx/sites-enabled/*;

pay attention on permission
the 1st edition of my.conf is root on /home/myusername/, but will get 403 Forbidden error, check the error.log:
2016/04/07 20:12:44 [error] 12466#0: *2 open() "/home/myusername/data/a" failed (13: Permission denied), 
client: 127.0.0.1, server: , request: "GET /a HTTP/1.1", host: "localhost"