Left-clicking on Display (in the bottom-right corner of the project's window) will show a sub-menu :
You will find functions you can make visible or not : Stencil, Paper, Selection, Animator Disk, Camera and Notes.
The Follow camera option will be explained in lesson 8.
The Display Settings window is accessible via the Windows > Show main menu and is used to choose the color and opacity of the guides, stencils, animation disk, etc.
You may also enable display of the stencil, paper and selections when using the latter.
You can change the opacity of the HUD Alpha and the Squiggles.
These notions will be explained along the manual.