Well, that was a quick look at a little bit of what EJB can do. As is, the chapter barely scratched the surface of everything you need to know to fully implement applications using EJB.
In summary, EJBs allow you to develop applications with centralized business logic that implement transaction processing, and they allow for synchronization between multiple applications.
An EJB has three components: the home interface, the remote interface, and the bean. Beans can be stateless, stateful, or persistent (entity) beans.
JBoss is an open source implementation of EJB that can be easily integrated with Tomcat.