A basic question of Lilypond

[wyanshan]

Hello everyone, 

I start to learn C++ programming half years ago and have just a little 
programming experiences before that.
I  played guitar in my free time and know basic theory of music. I found 
LilyPond!

I have a very basic question about lilypond, maybe basic, but I think basic 
questions and answers would be to way for those who want to open a door of a 
new world. Thanks ahead.

Where is the start up window file is in the source code? (The start up window 
means the window when you open the software). For example with excel VBA, I 
create a window file named with myWindow.frm,
So the my Window.frm (with extension name frm) is saved, I can find it.  I 
think I have downloaded the source file I can find lilyPond GUI design file and 
the scheme of this window loading process, and also design of menus, I tried
But I can’t find it.   
So, would some friend teach me the lilyPond software startup theory and how to 
design the GUI look.

Fortunatelly, I found the Untitled file is in the directory of ‘ly’ with file 
name welcome-to-LilyPond-MACOS.ly <http://welcome-to-lilypond-macos.ly/>, which 
means I am not very foolish.

I really suggest there should be a very basic manual telling programming 
beginners the very basic software startup theory and GUI design and the inter 
relationship among the sourcecode.
Maybe you think these things is too basic, but I think this is import...