If you want to run the slides project yourself, you'll need a copy of the Java 8 SDK and Leinengen on your computer. How you get those is up to you. Once you have them, you can run:
lein run -m clojure.main scripts/repl.clj
Which will boot up the figwheel app and drop you into a repl. You can now page through the slides at http://localhost:3449. Any changes you make to the clojurescript files will be hot-reloaded. You can do the same for CSS if you install sass and run build.sh alongside the repl.
The deck was built with the Cursive plugin for IntelliJ Idea. If you want to use that environment, you can download Cursive and set up a new run target using these instructions on the Figwheel wiki. This will provide a somewhat better development experience.