Module serves as a container of different parts of your app such as controllers, services, filters, directives, etc. Modules can be referenced by other modules through Angular's dependency injection mechanism.

Creating a module:

angular
    .module('app', []);

Array [] passed in above example is the list of modules app depends on, if there are no dependencies then we pass Empty Array i.e. [].

Injecting a module as a dependency of another module:

angular.module('app', [
    'app.auth',
    'app.dashboard'
]);

Referencing a module:

angular
    .module('app');

Module is a container for various parts of your applications - controller, services, filters, directive, etc.

Why to use Modules
Most applications have a main method that instantiates and wires together the different parts of the application.
Angular apps don't have main method.
But in AngularJs the declarative process is easy to understand and one can package code as reusable modules.
Modules can be loaded in any order because modules delay execution.

declare a module

var app = angular.module('myApp', []);
// Empty array is list of modules myApp is depends on.
// if there are any required dependancies, 
// then you can add in module, Like ['ngAnimate']

app.controller('myController', function() {

  // write your business logic here
});

Module Loading and Dependencies

angular.module('myModule', []).
config(function(injectables) {
  // here you can only inject providers in to config blocks.
});

angular.module('myModule', []).
run(function(injectables) {
  // here you can only inject instances in to config blocks.
});