One of the most important concepts that you need to know about Java EE is: it is a standard. If you go to the Java Community Process (JCP) website, you will find the Java Specification Request (JSR) for the Java EE platform (for Version 8 it is JSR 366).
A standard... for what? Well, for an application server! For instance, a Java EE application server.
It means that you can develop your Java EE application knowing it will run in an environment that provides a bunch of resources that you can rely on.
It also means you can easily move from one application server to another, as long as you stick to the Java EE patterns instead of some vendor-specific feature (considered a bad practice). Your application should have the same behavior ...
