This workshop uses the wonderful Ellie App for running Elm demos and exercises. Ellie is to Elm what JSBin or JSFiddle is to JavaScript.
All you need is a modern browser such as Chrome or Firefox. Verify your OS and browser can use Ellie by trying to compile this URL: https://ellie-app.com/TPL2qc9ca1/0. I've seen problems with some Linux distros in the past.
For more information and links to the demos and exercises we will use, visit https://github.com/jfairbank/elm-workshop.