You can view the course materials in an non-iteractive fashion directly on Github, for example: session 1.
To get the course materials running interactively, you need to download the course files and run them with Jupyter (previously known as iPython).
The easiest way to get a working version of Jupyter on Mac OS X is to download and run Pineapple.
The materials can be downloaded from Github using the "Download ZIP" button.
In order to get the interactive widgets working in Pineapple, you need to open this file and click "Run All".
In [ ]:
import pineapple
%require ipywidgets