How to solve the problem with the transition?

Question

PHP

When switching from an html document to a php document, the whole code is shown, and not a specific line, how can this be solved?
Here is the php code:

<?php
  if (empty($_POST['name'])) {
    exit('Некорректное имя пользователя');
  }else{
    spliti('', $_POST['name']);
  }
   ?>

When you click on the submit button on the html page, it just shows the full php code, not a specific line

Answer 1

Enable PHP processing on the web server

Answer 2

File extension must be php