To use: when you have the dependancies as per
the docs you should run
bundle install.
HTML files are based on Minima - if you need to configure the post or page layouts, copy those files in as needed.
Bootstrap variables can be overriden in _sass/custom.scss - refer
to the full list of available values.
Note that GitHub Pages doesn't run gems that aren't on their predefined list, so it won't work with their autocompile, you'll need to push up and serve the compiled files.