Hi,
You don't need the source code to setup a web site, the demo site is just a normal installation of the pre-compiled mojoPortal package that you can get on our codeplex download page. It also has some of our commercial add on features and these are available in our store.
The pages and content on the demo site are just example content, you can create pages and content using the built in features of mojoPortal, it is very easy once you learn how to use it.
The source code for mojoPortal is available but the main uses for source code are for learning how it works and for good example code to help you learn how to build custom features.
The content of the demo site has nothing to do with source code, content and pages can be created right from your web browser.
Hope that helps,
Joe