Basics displaying strings

<div ng-app="my_app" ng-controller="my_ctrl">

First Name: <input type="text" ng-model="f_name"><br>
Last Name: <input type="text" ng-model="l_name"><br>
<br>
Welcome : {{f_name + " " + l_name}}

</div>

<script>
var app = angular.module('my_app', []);
app.controller('my_ctrl', function($scope) {
  $scope.f_name= "Robort";
  $scope.l_name= "King";
});
</script>