What category of app are you looking to write, narrowing down the class "app with a GUI" a little?

I don't think this should matter for your answer, since it's just a barrier toward a broad class of programming I'm trying to overcome.

Can you name a specific example of one you've tried to compile and run, and you've been confused at the result?

All of them ;-) but I'll give you a specific example when I get back to my home computer.

One general hint is that a good way to learn how to code up significant programs from scratch is to, first, get a significant program that works and modify or extend it in some way.

Well, that's kind of hard when they don't run even when you compile them. But on top of that, I haven't found any multi-source-code-file in which it's easy to jump to just the part of the code that implements a particular feature, usually because of poor documentation.