Sass

two formats

.scss is superset of CSS, every valid CSS is valid SCSS

#main {
  color: blue;
  font-size: 0.3em;
}

.sass uses indentation instead of brackets and semicolons

#main
  color: blue
  font-size: 0.3em

Sass maps

sass map:

$map: (
  key: value,
  other-key: other-value
);

bootstrap-sass

when you work with bootstrap-sass, use the following structure in your main .scss file (copied from roots sage project)

your custom variables come first, then import _bootstrap.scss, then any other files

@import "common/variables";

// bower:scss
@import "../../bower_components/bootstrap-sass/assets/stylesheets/_bootstrap.scss";
// endbower

@import "common/global";
@import "components/buttons";
@import "components/comments";
@import "components/forms";
@import "components/grid";
@import "components/wp-classes";
@import "layouts/header";
@import "layouts/sidebar";
@import "layouts/footer";
@import "layouts/pages";
@import "layouts/posts";
@import "layouts/tinymce";