You can use Glade to design and adjust your user interface. You still must write some Euphoria functions to respond to user interactions with the GUI. This is no different than VisualBasic, Delphi, or other programming environments, except that EuGTK code is generally less confusing.
For writing that Euphoria code, either Geany or Pete Eberlein's new WEE editor (written in Euphoria and using EuGTK) works for me. If you test-run your program from an x-term, EuGTK will generate function prototypes for missing functions and display them on the terminal. You can then copy and paste the prototype code into your program, and add the necessary details.
Please start by reading Glade docs, Starting Glade, and Starting Glade II.
Some of the programs in this folder are duplicates of other demos elsewhere, but have been re-written using Glade to design the user-interface. These are provided as examples f.y.i.