Of these, which are Facing Pages typically used for?

Paragraph Styles:

Definition of a font?

InDesign provides a shortcut editor in which you can view and generate a list of all shortcuts, and edit or create your own shortcuts.

The Application Bar includes:

How do you add a page in a layout?

Object Styles panel is to create, edit, and apply object Styles that is the collection attributes and effects applied to any object.

What does the highlighted tool labeled as A in the image above do?

It is possible to create unequal column widths for columns in a text frame.

Which can be linked between two documents or within the documents?

In which CSS option under EPUB Advanced options can you create a list of CSS Styles that can be edited?