The compojure template provides a working webserver and simple webapp out of the box.
Run the project to start the server and webapp
lein ring server
If you have not used Compojure or Ring previously, then it may take a few seconds to download their libraries from the Internet before starting the Jetty web server.
You should see a output after the leiningen command showing you that the server has started
2016-07-15 13:44:02.242:INFO:oejs.Server:jetty-7.6.13.v20130916 2016-07-15 13:44:02.313:INFO:oejs.AbstractConnector:Started SelectChannelConnector@0.0.0.0:3000 Started server on port 3000
Your default browswer should also open at http://localhost:3000 with a message saying "Hello World". If your browser does not open then check for errors in the terminal where you ran the leiningen command.