An SSL certificate is generated and obtained for your host name (for example, "www.yourwebsite.com"), which is setup on the server.
Pages on your website are then securely accessible via a secure URL page (through a URL that begins with "https://" instead of just "http://").
When a visitor securely accesses your website, the server automatically sends your site's digital certificate which authenticates it.
The visitor's web browser then generates a unique "session key", which it encrypts with your site's public key, establishing a secure session with your website.
With a secure session established, any information can be submitted securely from your visitor, across the Internet, and to your website. It all takes only seconds and requires no action by the user. Depending on the browser, the user may see a close padlock icon, indicating that the session is secure.