... a TYPICAL sketch ...
So are we talking about "typical sketches" or are we talking about "C/C++ programs"?
"setup" and "loop" have no inherent meaning in C or C++; they are just function (subroutine) names used by the Arduino environment.
divided into three sections? Global, Setup and Loop?
"setup" and "loop" are not sections. They are function definitions for functions named "Setup" and "Loop" - if you want to get the deeper understanding, you need to start separating things that are part of the language from things that are defined by the environment.
A C program has essentially TWO parts:
variable_declarations
- function_declarations*
And then there are syntax definitions for each of those.
A variable_declaration looks something like:
variable-type name optional_initialization ;
And function_declaration looks like:
function-type name ( optional_parameter_list ) compound-statement
and compound_statement is:
{ statement_list }
(which is (one place) where the braces show up.)
The compiler folks have a standard syntax for specifying this sort of thing ("BNF") that further defines all the little parts (function-type, statement-list, etc) (recursively) until you get down to individual characters or tokens. You can fit the entire definition for C on a couple of pages.
(it gains some complexity; my examples above are "simplified.") C, as a language, pre-dates a lot of the "science", so its definition is a bit ugly. A "mini-pascal" definition fits on a single page.
How long has Arduino been out, 10 years? In 10 years no one has been able offer a simple explination?
Which "question" are you looking for a "simple explanation" for, again?
The simple explanation is "an Arduino Sketch is a simplified C program. For details, learn C."
C has been around for about 50 years. You've been given "simple explanations" several times, now, I thinkm, but you keep throwing in complications "what about Setup vs Loop, and global variables" (and other people keep throwing in complications as well.) "For details, learn compiler design. (hint: it's not actually simple.)"