full-screen backgrounds for pages & posts, transparent containers

hey. I am trying to understand the DESIGN qualities of WordPress.

how do I create a full-screen background for an individual page?
and, along these lines, how do I create transparent containers which look like they float above that background?

on a * fundamental * level i'm striving to understand how to fill the backgrounds, looking for visual composer plugins or other things. trying to understand the design quality.

is this related to 'custom post types' and 'content management' as a concept?