The simplest way to launch an RWT application is to run it using an RWT Application launch configuration. This launch configuration type uses information derived from the workbench preferences and your applications's Java project to launch the program.
You can also launch an RWT application by selecting a project instead of the compilation unit or class file. You will be prompted to select a class from those classes that define an entry point. If only one class with a main method is found in the project, that class is launched as if you selected it.
How the generated launch configuration can be altered, you can read in the topic Creating an RWT Application launch configuration.