I'm somewhat lost where to go for a decent tutorial on modern C.
Well, to be clear, Pelle's C is a plain C(11) compiler, nothing remotely C++. C and C++ are (should be treated as) completely different programming languages.
Pelles seems to assume programming knowledge for Windows a la MSDN.
As far as programming in C goes, no. You can write C program for console applications pretty much without any knowledge of Windows.
As programming for a target environment like Windows is/can be incredible complex, it is hard to include lessons for that in a free compiler. Pelle seems to have been busy enough to keep the compiler itself up to date.
As a general note, if I have to get down to such Windows basics, I usually fall back to (one of the earlier editions of) "Programming Windows" by Charles Petzold. Should be pretty much "the book" on programming for Windows.
My experience was some years ago with TurboC and AZ86 and I haven't written a function in C since.
Some experience with PHP which I find straightforward.
As long as you write proper ANSI C, you can do the same with Pelle's C.
What I find somewhat baffling is the HWND (hwnd), WINAPI stuff.
OK so they're the same as say, printf() but several layers removed. Right?
The basic problem is that with that, you are programming more for a specific environment (Windows in this case) rather than with a specific programming language.
Programming in a specific programming language and programming for a specific (user) environment are two different skill sets, that's something a lot of times people seem to overlook.
And as far as PHP goes (as you mentioned that you are/have been using it), it removes a lot of that by targeting a more common user environment, a web browser, which is (more or less) agnostic to the actual user environment being used (as in M$ Windows, Mac OS X, Linux KDE/Gnome/xfec/<etc>).
I recall many, may years ago trying to understand calculus which baffled me in the same way until one day a senior tutor sat down and in 15 minutes ... BINGO!
I'm clearly missing something so I need something like that experience here.
Well, things have been becoming more complex (and ever changing) since the days of Turbo C and Aztec C 86, where your only user environment was DOS.
I personally don't use Pelle's C for any Windows GUI based development, just mainly for console applications, sometimes even cross platform (Windows, Linux, DOS) and use a different programming environment (and programming language) for the very reason not to bother (too much) with the user environment specifics in GUI work that for me is always cross-platform (Windows, Linux and Mac OS).
Ralf