What's the main difference between Java SE and Java EE?

As far as the language goes it is not as though java changes. Java EE has access to all of the SE libraries. However EE adds a set of libraries for dealing with enterprise applications.

Java EE is more like a "platform" or an general area of development.

In Java SE you write applications that run as standalone java programs or as Applets. In JavaEE you can still do this, but you can also write applications that run inside of a Java EE container. The container can do a great amount of management for you such as scaling an application across threads, providing resource pools, and management features.

Java EE has a web framework based upon Servlets. It has JSP (Java Server Pages) which is a templating language that compiles from JSP to a Java servlet where it can be run by the container.

So Java EE is more or less Java SE + Enterprise platform technologies.

Java EE is far more than just a couple of extra libraries (that is what I thought when I first looked at it) since there are a ton of frameworks and technologies built upon the Java EE specifications.

But it all boils down to just plain old java.