Examples included in the source tarball
The distributed sources include some examples:
The examples can be found in the directory code/examples.
A complete application: WTimer
As a real-life demonstration I have written a complete application for WDialog: WTimer allows the user to edit time sheets that are stored in databases. The application is complete, and proves that a real-life application can actually be developed.
WTimer is not a simple program, but I think it is well-structured, and you can immediately understand which module implements which feature. The code is sometimes tricky, however, as complicated user interactions must be processed. So I think it is not a good idea to read this example as the first one, but it serves as an illustration how to combine the elementary features of WDialog to get non-trivial effects.
You can find more information about WTimer on the project page.