Mozilla Prism enables you to create shortcuts to your favorite online apps (Gmail, Facebook, Twitter, etc.) directly on the desktop, the Start menu or the Quick launch bar. The process of shortcut creation is a bit rudimentary – you have to enter all the info by hand – but is quite simple as well.
Once the shortcut is created, just double click it as any other regular Windows shortcut and you'll open a stripped-down browser window with the selected online app already loaded in it.
Despite being based on an interesting concept – blurring the lines between desktop and online apps – I don't really see how using Mozilla Prism is better than using your standard web browser to access your favorite online apps. The only advantage I can think of, if any, is to make these tools easier to access for people with limited computer knowledge.
Mozilla Prism is an interesting project that tries to bring both desktop apps and online apps together, but it still has a lot of room for improvement.