There are a few different options to getting Minnow setup. In the end it really just depends on how you intend to use it. Currently Minnow is released with the Sass (SCSS) source and compiled CSS (Regular & Minified).
If you prefer to install manually you can browse the latest builds on GitHub.Download via Github Releases
Minnow can also be installed via the Bower Package manager. If you are unsure how to use that, then reference the Bower website.
bower install minnow-css