HTML:

 <form method="post">
         <div class="form-group">
         <input type="text" class="form-control" placeholder="Ваше Имя:" name="name" required><br>
         <textarea class="form-control" rows="3" name="text" required></textarea>
         </div>
         <button type="submit" class="btn btn-primary" name="submit">Отправить</button>
         </form>

PHP:

//Добавление комментария к статье
function add_comment($connect){
	$post_id = (int)$_GET['post_id'];
	if(isset($_POST['submit'])){
		$name = trim(htmlspecialchars(mysqli_real_escape_string($connect, $_POST['name'])));
		$text = trim(htmlspecialchars(mysqli_real_escape_string($connect, $_POST['text'])));
		$sql = "INSERT INTO comments (`name`, `text`, `post_id`) VALUES ('$name', '$text', '$post_id')";
		$result = mysqli_query($connect, $sql);
		header("Location: ". $_SERVER["REQUEST_URI"]);
	}
}