javaFxPart1: Tweak intro to JavaFX GUI structure

Adapated from #89 by @laney0808

tutorials/javaFxPart1.md

@@ -7,13 +7,18 @@
 
 # JavaFX tutorial part 1 – Getting started
 
-## Lifecycle of a JavaFX  application
+## The structure of a JavaFX  GUI
 
-Imagine yourself as a director of a play. First you provision the props that you will feature in your play. These can be hand props for your actors to interact with or even set dressings just to liven up the background. You then decide where to place the props for every scene. With a proper script in hand, you can finally approach a theatre and request for a stage. Thereafter, it’s just a matter of pulling the curtains on your masterpiece.
+A JavaFX application is like a play you are directing. Instead of creating props, you create `Node`s (`Node`s are the fundamental building blocks of a JavaFX application), and place them onto a `Scene` (a scene is a graph of `Node`s). Then, you set your `Scene` on a `Stage` provided by JavaFX. When you call `Stage#show()` method, JavaFX renders a window with your `Stage` on it.
 
 <puml src="images/javafx/JavaFxHierarchy.puml" />
 
-A JavaFX application is like a play you are directing. Instead of creating props, you create `Node`s (`Node`s are the fundamental building blocks of a JavaFX application), and place them onto a `Scene` (a scene is a graph of `Node`s). Then, you set your `Scene` on a `Stage` provided by JavaFX. When you call `Stage#show()` method, JavaFX renders a window with your `Stage` on it.
+More specifically,
+
+* the `Stage` is like a window in a desktop application. It is the top-level container for a JavaFX application.
+* a `Scene` is a container for `Node`s. A stage contains multiple scenes, and shows different scenes at different times based on programme state, user actions, etc.
+* a `Node` is a component that can be added to a `Scene`. `Node`s can be simple controls like `Label`, `Button`, etc., or complex controls like `TableView`, `TreeView`, etc. A `Node` can contain other `Node`s too.
+* a `Root Node` is the topmost `Node` in a `Scene`, the parent of all other `Node`s. It is usually a pane like `StackPane`, `BorderPane`, etc.
 
 Well, that's a very high-level view of how JavaFX works. The actual implementation of a Java FX is a bit more (ahem...) "involved". This tutorial takes you through the steps of building a typical Java FX application, using a chatbot application called Duke as a running example. Given below is what the end result can look like if you follow this tutorial until the end: