Teaching myself how to handle Atahualpa - Suggestions Pls

Hello everyone, I'm completely new to using WP and want to set up a site using Atahualpa. While I see it's rather complex for a newbie I still want to be able to understand it well so I would like to ask you what should I teach myself to handle this theme well; would CSS be enough (I already know html)? What else would be necessary?

Thank you!