In order to make an SSL connection, the SSL protocol requires that a server should have a digital certificate installed. A digital certificate is an electronic file that uniquely identifies individuals and servers. Digital certificates serve as a kind of digital passport or credential which authenticate the server prior to the SSL session being established. Typically, digital certificates are signed by an independent and trusted third party to ensure their validity. The "signer" of a certificate is known as a Certification Authority (CA), such as thawte.
The most common application of SSL certificates is to secure data transfer between web browsers and web servers. Although SSL may be used to secure server to server communications, this guide will make use of browser-server examples to explain the workings of SSL.