Force.com Sites lets you create public web applications and web sites that run natively on Force.com - under your own domain. Force.com Sites lets you easily extend the reach of your existing applications to new, external audiences, and your site visitors don't need to authenticate to view your pages. In fact, if you're already using Visualforce to create your user interfaces, it's a simple matter of bundling them into a Force.com Site to create a public web application.
Some key features of Force.com Sites include:
To begin learning about Force.com Sites, follow this path.
Here are some other helpful resources for Force.com Sites.