You need Git and NodeJS installed on your computer. You also need Python, this is required by the node-gyp dependency used by node-sass.
Create a new folder for the project and open a terminal there to execute the following commands.
npm init
npm install isometricsass --save-dev
Now just paste this in your style.sass file:
@import isometric
Now you can create your own 3D objects by using or extending the Sass classes in the _isometric.sass
file.