Calling Root Methods from Other Classes

Ok, I’ve experimented several different ways & cannot figure out how to access Methods in my main class from an object created by a custom class. I’ve created (okay borrowed liberally) a class that preloads images, which checks when the images are all loaded. All I want is to have this class fire a method in my Main Class when it knows all the images are loaded. I can’t find a way to access methods directly in my main class, or thru a parent reference, etc. What am I not understanding fundamentally & what how do I access methods across instances & classes?