Java: get started with the JavaFX GUI in Eclipse
JavaFX is the preferred GUI toolkit for new projects at the moment.
Create a new Java project.
Add the jar:
(Right-click on your project) > Properties > Java Build Path > Add External JARs
Browse to your JRE's lib folder and select jfxrt.jar
Create a class that uses it.
(Right-click on your project) > New > Class
Google "JavaFX Hello World" and paste it into your new .java file.
Press the green (>) run button to compile and run your project.