As a beginner, I read few chapters in the Flutter Apprentice book. I really felt comfortable with the content. Although I only know dart basics and some knowledge of Object Oriented Programming , I was able to understand every single concept and code very easily.
After reaching chapter 5 (about scrollable widgets) , I realized that in order to understand the concepts, I have to go to depth in OOP and asynchronous programming.
Currently I am learning dart in depth. If you are a beginner , I strongly recommend you to learn the OOP and asynchronous programming from start itself.