Hello,
Scooter uses sitemesh as the default, you may want to take a look at decorators.xml and sitemesh.xml.
It's gonna be on the decorators.xml where you will find the templates, In the 'twitterdemo' it is those which has those '<pattern>' tags in the decorators.xml.
A simple explanation on how it works is that, you will just call your page in the request like 'main.jsp', and sitemesh will just present the page , inserting your main.jsp in the specified template based on your decorators.xml.
HTH