I've been developing web apps, for a while now so i know how to get the job done, what i don't know is how every thing really works, i know some but the rest i can't get a grasp on like how abstract works, what happens when i instantiate an object from a class that inherits from an abstract class?, where things get stored Heap vs Stack?, in other words the Interview questions that i suck at, so any advice would be great, books, videos, online courses, whatever you can provide would really help me.