Winapi 32

Hello,
I am studying how to create windows programs and I was wondering how important it was to study the functions, structures, etc. . The book said I did not have to study how to create the window (the code), but will you use these functions in anything besides the default window? Or is it just to create the window? Thanks

winapi is used whenever you need to interact with windows (as in the operating system, not the display element).

So I should memorize the functions, but not necessarily the whole 80 line you need for all programs. (BTW I am using the book by Petzold)