hey @kartik,
In order to route to any custom URL or displaying message when user attend to certain unspecified route path,there are generally two ways to define in $stateProvider which is used to configure the UI-router.
The code is as follow:
var app= angular.module([$stateProvider , function($stateProvider){
      $stateProvider 
      .state('root', {
      url: '/',
     template:  '<strong> You are at root....</strong>
       }
     
     .state('noroute', {
      url: '*path',
     template:  '<strong> No Root Available...</strong>
       }
}]);
In order to redirect to existing route when no route found, the above code can be discard and include the $urlRouterProvider as follow:
var app= angular.module([$stateProvider , $urlRouterProvider, function($stateProvider, $urlRouterProvider){
      $stateProvider 
      .state('root', {
      url: '/',
     template:  '<strong> You are at root....</strong>
       }
     urlRouterProvider.otherwise('/');
}]);