Recently I started to have a look at the GTK library in C, and wanted to create GUI application. In fact, I want to create an image application, but I don't know how to make my application looking exactly the same as my drawing, I've looked throught the gtk3-demo and also the widget factory but problems remains; How to create GUI application, how do I know which container should I use, how do I know what kind of widget ? etc... So I have a picture of what I want to do, but I have absolutly no idea how. What is the process, what question should I ask myself in order to get my GUI application done ?
Drawing of my application
I would very much recommend you play with the Gtk3 GUI using python. You can interactively create windows, containers. Even later, it is much faster to develop the GUI in python, as many have already experienced.
Most of the Gtk3 C/C++ tutorials are available in Python too.
Glade is excellent in many cases - particularly if you want only standard behaviour of the widgets. If you even slightly wander from that straight path, things can get complicated quickly.
If it is really necessary, there are several ways to incorporate C/C++ functions into the Python GUI to make those critical apps go faster.