Question: Tomcat only implements the *web container* of the Java Enterprise Edition architecture. In contrast, e.g. GlassFish implements a *full Java EE stack*. This [has been discussed](https://stackoverflow.com/questions/3821640/what-is-difference-between-tomcat-and-jboss-and-glassfish) a lot on stackoverflow.

However, for a Java EE beginner like me it is hard to imagine what cannot be done with Tomcat. Could you please give some short examples?

Answer: 
There are a large number of technologies/capabilities that are part of Java EE. Some of them are available as part of the Tomcat download, others can be added to a Tomcat based environment and some cannot be added to a Tomcat environment.

Deploy an EJB jar onto Tomcat: No.

Call Remote methods of an EJB running in an EJB container: Yes.

Deploy a RAR onto Tomcat: No.

Deploy an EAR onto Tomcat: No.

Deploy an Application Client jar onto Tomcat: No.

Cobble together a way to host a Java Web Startable app that calls Remote methods of an EJB running in an EJB container: Yes

Use JSF as the framework for your app: Yes, but you need to package an implementation in your app or install it onto your server.

Create a program that leverages JSR-88 to manage deployment of war files onto Tomcat: No... not that this is a huge loss.

Use JSR-77 MEJBs to manage your Tomcat server: No... another not huge loss.

Create web apps that provide SOAP web services: Yes... but you will need to get the tools and libraries as part of a separate download and integrate them with your workflow, application and server runtime yourself.

Create web apps that use JPA: Yes... but you will need to the tools and libraries as part of a separate download and integrate them with your workflow, application and server runtime yourself.

Create web apps that use CDI: Yes... but you will need to the tools and libraries as part of a separate download and integrate them with your workflow, application and server runtime yourself.
EJBs - Stateless Session Beans, Stateful Session beans
Message driven beans
EJB Timers
JPA (EJB3.0)

This is a very basic list. there are many more features that Tomcat doesn't have.