What is the difference between nginx config files? [closed]

I have noticed that nginx has a number of configuration files such as nginx.conf in the /etc/nginx directory and 2 others one in the /etc/nginx/sites-available called default and one in the /etc/nginx/sites-enabled called also default. Does anyone know what is the difference between all those?

Thanks in advance!

In ubuntu by default the site config is from /etc/sites-available, I believe.