running javascript koans on github

Dumb beginner question...how do I run the Javascript Koans on the following site?

http://ift.tt/1M0XKDc

I follow the directions on the 'readme' doc, but it just opens up some code, and I can't do anything from there.

Can somebody please give me a quick walkthru on how to do execute those Koans? Do I need to download some type of software? Any help is much appreciated.

Cheers,

Anthony