SSL certificates are needed when you want transmissions on the wire to be secured. This is indicated by the "https" (as opposed to "http") in the browser address bar as well as a "lock" icon shown on the browser.

A SSL certificate and secure connection is needed if you are accepting credit card information directly on the site, for example.

Shared SSL Certificates

Some shared webhosts will provide you with shared SSL certificates. That mean that a single certificate is shared with many website owners. This is fine if you are just learning about SSL and testing; but consider purchasing an individual SSL certificate depending on your situation.

For example, hostmonster shared SSL certificates are in the form...
https://secure.hostmonster.com/~yourunixusername/
(more detail on hostmonster's helpdesk).

Where to Get SSL Certificates

For a production eCommerce site that accepts credit card information directly, it is best to purchase a dedicated IP address from your webhost and purchase an individual SSL certificate.

You can purchase them at Verisign, DigiCert, Thawte, GeoTrust, NetworkSolutions, GoDaddy, and other places.

Depending on your web host, you may be able to purchase it from them.

Learn More

To learn more about SSL certificates, browse through Verisign's SSL Information Center.