Make sure to have Xcode installed.
Type npm install. Then type grunt, which will prompt for a password since it needs root access to install global dependencies.
When that script finishes an iOS simulator should pop up displaying "Hello World!". If it doesn't pop up immediately, look for the app called HelloWorld and open it up.
Now navigate to /build/index.html in your browser. You should also see "Hello World!" displayed in the browser.
To Build: grunt
To Develop: grunt watch
To Test: grunt test
To Build PhoneGap App: grunt phonegap