The Page builder can be broadly classified into 3 sections :
Blocks & templates panel
Canvas
Customise & Layers panel.

The Blocks and templates panel [RED] contain all the building blocks for your Pages
The Canvas [Blue] is the Page how it looks outside the page builder content
The Customize & Layers panel, contain all the layers and customisation options for various blocks.
In subsequent docs we’ll see how we can use them effectively to design our pages, easily and efficiently.