Sorry it isn't clear to you, we could definitely do a better job with the README. If you look on the website[0] you'll see actual examples of usage. (I just announced this project on stage at ReactLondon during my talk, so it's very fresh and we haven't had a lot of time to clean up the docs yet)

Basically, there is lots of styles in JavaScript libraries floating around, especially in the React ecosystem. The issue is that many people need Sass utility functions and mixins like lighten/darken/clearfix to be productive with their styling, and no real comprehensive "Compass for styles in JavaScript" exists—so this is it.

We looked at a lot of existing JavaScript color libraries, but most of them have some sort of fluent API that is very different from the way CSS preprocessors handle these functions. This confuses people and makes the API hard to learn, so we decided to build our own that mimics the Sass API as closely as possible. (apart from being all curried functions that are composeable, which means switching some argument orders around)

[0]: https://polished.js.org