Possible to create Upfront themes from scratch?

I've installed Upfront and the apparent child themes: Fixer, Scribe and Spirit. After installing these, it appears that I can only apply and customize the three child themes and that Upfront itself must be a support theme facilitating the others... unless it is possible to create new themes from scratch that I'm not seeing?

Is it somehow possible to design a site from scratch with Upfront without starting from one of these base themes?

Further, can you direct me to some documentation that can answer various usage questions? So far my experience with Headway seems a little more intuitive vs what we have here with Upfront, but I suspect that I am missing some key understanding here at the beginning of my efforts with it.