Frustrated!!!! I can't even figure out how to make changes to my theme

I've been trying to use the community and the videos to figure out how to make changes to my site - but I'm getting nowhere. None of the changes/edits I make stick, even after 'updating'. I can't figure out how to widgetize my site (Spirit theme) because I don't know where to find the functions.php file. I can't figure out how to get the menu we imported from our old WP.com site to work on the new site. I've spent hours working on these things and I'm getting nowhere.