How ng- module work?

<!DOCTYPE html>
<html>

<head>
  <script src="https://code.angularjs.org/1.3.14/angular.js"></script>
  <script>
    var app = angular.module('myApp', []);
    app.controller('myAppCtrl', function($scope) {
      $scope.sms ="Hello Ng  Module....";
    });
  </script>
</head>

<body ng-app="myApp">
  <div ng-controller="myAppCtrl">
    <div>
      <h2>{{sms}}</h2>
    </div>
  </div>
</body>

</html>

// Code goes here

/* Styles go here */