Please link to the stylesheet in the
<head> of your application:
<link rel="stylesheet" href="https://design.smart.coop/css/main.css">
Go to the component documentation, and find the component you need.
Copy paste the HTML (or Pug if you are using this template language), and you are on your way to create an app.
If you use the Pug templating language in your own project, you will need to include the mixins in your global namespace in your app. You can find the mixins here. There is a very specific icon mixin which you can find here.
You can fork this pen to get started, it contains the right settings.