Iam a newbie to programming

<?php  
 $message = '';  
 $error = '';  
 if(isset($_POST["submit"]))  
 {  
      if(empty($_POST["name"]))  
      {  
           $error = "Enter name";  
      }  
      else if(empty($_POST["datedon"]))  
      {  
           $error = "Enter Date";  
      }
      else if(empty($_POST["timeon"]))  
      {  
           $error = "Enter Time";  
      }  
      else  
      {  
           if(file_exists('try.json'))  
           {  
                $current_data = file_get_contents('try.json');  
                $array_data = json_decode($current_data, true);  
                $extra = array(  
                     'name'               =>     $_POST['name'],
                     'datedon'     =>     $_POST["datedon"],
                     'timeon'     =>     $_POST["timeon"],  
                );
                $array_data[] = $extra;
                $final_data = json_encode($array_data);
                if(file_put_contents('try.json', $final_data))
                {  
                     $message = "Deals Added Successfully<p></p>";  
                }  
           }  
           else  
           {  
                $error = 'JSON File not exits';  
           }  
      }  
 }  
 ?>