SSL (Secure Sockets Layer) is the standard security technology for establishing an encrypted link between a web server and a browser.
This link ensures that all data passed between the web server and browsers remain private and integral.
To be able to create an SSL connection a web server requires an SSL Certificate.
You can either buy your own certificate, or use a free one from a SSL certificate provider.
This is important because the information you send on the Internet is passed from computer to computer to get to the destination server.
Any computer in between you and the server can see your credit card numbers, usernames and passwords,
and other sensitive information if it is not encrypted with an SSL certificate.