A CA-signed certificate provides advantages. First, browsers are built with
data about most CAs and automatically recognize a signature from one of
them on your certificate most of the time. A self-signed certificate will cause
the browser to display a rather scary-looking (to a nontechnical person)
warning and require the user to acknowledge it before viewing your site. In
addition, when the CA issues the signed certificate, it is guaranteeing the
identity of the organization providing the web pages.
To learn more about certificates and keys, including installation of keys and
certificates you pay for, see http://tldp.org/HOWTO/SSL-Certificates-
HOWTO/index.html.
Reference
http://nginx.org/en/docs/—The Nginx wiki website, where you can find
extensive documentation and information about Nginx, including
installation instructions, downloads, and tips for configuration and use