How to create a self-signed SSL Certificate ...
... which can be used for testing purposes or internal usage
The following is an extremely simplified view of how SSL is implemented and what part the certificate plays in the entire process.
Normal web traffic is sent unencrypted over the Internet. That is, anyone with access to the right tools can snoop all of that traffic. Obviously, this can lead to problems, especially where security and privacy is necessary, such as in credit card data and bank transactions. The Secure Socket Layer is used to encrypt the data stream between the web server and the web client (the browser).