in the tutorial they said
Open the "Source/Main.hx" file in the editor of your choice. It should look something like this:
but i don't where is that file?
On Windows, if you run "openfl create project HelloWorld" and cmd points to
C:\Users\YOUR_USERNAME\the project directory will be
C:\Users\YOUR_USERNAME\HelloWorld\Source\Main.hxIt depends what directory is in cmd when you run that command.