GUI interface for engineering modeling

[cyrus khazaei]

Dear All:
In softwares such as Autocad,Etabs(civil eng),Sap,Safe,Plaxis(Geotech eng.),FLAC and ... that are based on Finite Element Method modelling or other methods,there is an interfase for user that can model a dam or building ot tunnel or foundation and ... by just choosing an item and click on interface to draw points,lines,surfaces...exactly like what we do in GUI builder for example in Netbeans.
I know you can't teach me how to build such interface here but please give me some keywords to search and learn.What part of graphical programing should I learn to build such interface for modeling in my finite element code.
Thank you All