Boots & Bones is built on three core principles (which should be familiar by now):
Skeleton is a small collection of well-organized CSS files that can help you rapidly develop sites that look beautiful at any size, be it a 17" laptop screen or an iPhone. It's based on a responsive grid, but also provides very basic CSS for typography, buttons, forms and media queries. Go ahead, resize this super basic page to see the grid in action.
The easiest way to really get started with Skeleton is to check out the full docs and info at www.getskeleton.com. Skeleton is also open-source and has a project on git, so check that out if you want to report bugs or create a pull request.