A Grease pencil starts like any other object (for example the Cube) in Blender, as a object.
And behaves like a object.
A single Grease pencil object can have multiple layers. Those layers have a sequence (in front, in back). But also the physical location where you start drawing.
The vending machine is a 3D object.
You can instruct grease pencil to draw on the surface of a object.
You have a Grease pencil modifier on a 3D object (vending machine), which draw for you the outlines.
It’s difficult to explain, that’s why I started doing online tutorial Grease pencil.
And Grease pencil is changing also, some tutorials are too old.
Currently, I’m trying to follow this Game Dev Drawing Course, using Grease Pencil.
I bought for this a pen tablet.