The document summarizes the directory structure and main components of a Struts 2 application. The ROOT directory contains JSP and other files while the WEB-INF directory houses important configuration files like web.xml and struts.xml. The classes subdirectory under WEB-INF contains class files and the struts.xml configuration file which defines actions, packages, and results and is the heart of the Struts 2 application. The lib subdirectory contains JAR files needed to run the application.