To get an idea of the Tonic Look & Feel in a running application, you can download the Tonic Demo. This is a small mock application which displays virtually all GUI elements available in Swing.
The application does not serve any other purpose, and offers no real functionality, except to demonstrate the Tonic features.
In order to run the demo, you need to have a JDK or Java Runtime Environment installed on your machine. To get Java, visit java.sun.com.