Simple Tutorial

I have inherited a project that uses Hibernate Tools to generate model classes from tables, and that currently works. However, I want to change the generated classes to extend a new abstract class rather than simply implement Serializable. I am hoping there is a simple tutorial somewhere that explains how the FTL files interact, and how I can change what is being provided by pojo.getDeclarationName(), pojo.getExtendsDeclaration(), etc.