Run "lein figwheel" in a terminal to compile the app. Wait a bit, then browse to http://localhost:3449.
Any changes to ClojureScript source files (in src) will be reflected in the running page immediately (while "lein figwheel" is running).
Run "lein clean; lein with-profile prod compile" to compile an optimized version.
Original reagent example code found at https://github.com/reagent-project/reagent