Run this command to get the code you will modify:

git clone https://github.com/lispcast/building-re-frame-components.git
cd building-re-frame-components

Figwheel is a ClojureScript compiler that watches your files and recompiles them. It also sends your code to open browsers. It lets you modify code in files, save it, and see the result instantly in your browser.

Running the Figwheel compiler is easy:

lein fig-dev

That should open a browser. If it doesn't, open http://localhost:3449 and you will see all of the components listed.