What is SSL, and how does an SSL Certificate work?

SSL stands for Secure Sockets Layer. It's actually an outdated term, as SSL was replaced by Transport Layer Security (TLS) a long time ago, but most people still refer to it as SSL anyway. It is a digital encryption protocol used to encrypt/secure information sent from a browser to a server, or server to server. SSL certificates are used to protect sensitive information like credit card numbers, usernames, passwords, email addresses, etc.

When a web browser connects to a server over the HTTPS protocol, the server sends a copy of it's SSL Certificate to the browser. The browser verifies the certificate against the Trusted Root built into the browser, and makes sure the server is who it says it is. Once verified, they pass each other keys to generate the session keys, and a secure tunnel is setup.