In general, I personally make it a point to refer *first* core documentation.
For Struts2 - http://struts.apache.org/188.8.131.52/docs/home.html
What we all do when starting something new, is to build a -helloworld- sort of application. Sometimes the documentation will miss a few things. In that case refer to the exceptions when Tomcat is loading the Struts2 application.
(And post how you solved it, for developers referring to it later know what the problem was and the resolution)