Please see my comment to the question.
Try to start here:
It's hard to explain why do I feel you are doing something wrong. You cannot just ask "what is polymorphism?", "what is inheritance?", etc., and learn something this way. It does not work this way. You have to learn all together, systematically. If you try to learn this here, that there, you won't catch the essence of thing.
Take a book, and read it from the beginning to the end, with a lot of attention, solving exercises as you go. Learn concepts, conceptions and techniques, all together.