HTMLにCSSとJavaScriptを使用させるには、CSSファイルとJavaScriptファイルをそれぞれ`<link>`タグと`<script>`タグを使ってHTMLファイルにリンクさせる必要があります。

以下はCSSとJavaScriptファイルへのリンクを含むHTMLファイルの更新版です：

```html
<!DOCTYPE html>
<html>
  <head>
    <link rel="stylesheet" type="text/css" href="signup.css">
  </head>
  <body>
    <form id="signup-form">
      <!-- form content -->
    </form>

    <script src="signup.js"></script>
  </body>
</html>```

ユーザーが入力した内容を記録するには、PHP、Node.js、Ruby on Rails のようなサーバーサイドの言語を使って、フォームのデータをデータベースかサーバー上のファイルに保存します。また、Google Forms、Wufoo、Typeformのようなウェブサービスを使ってフォームを作成・管理することもできます。

PHPを使ってフォームデータを処理する例を示します：

```php
<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
  $firstName = $_POST["first-name"];
  $lastName = $_POST["last-name"];
  $email = $_POST["email"];
  $phone = $_POST["phone"];
  $password = $_POST["password"];

  // Store the form data in a database or as a file
  // ...

  // Redirect the user to a thank you page
  header("Location: thank-you.html");
  exit;
}
?>```

そして、PHPスクリプトにフォームデータを送信するJavaScriptファイルの更新版です：

```javascript
const form = document.querySelector("#signup-form");
const passwordInput = document.querySelector("#password");
const passwordConfirmInput = document.querySelector("#password-confirm");

form.addEventListener("submit", (event) => {
  event.preventDefault();

  if (passwordInput.value !== passwordConfirmInput.value) {
    alert("Password and password confirmation do not match.");
    return;
  }

  form.action = "signup.php";
  form.method = "post";
  form.submit();
});```

これは基本的な例であり、フォームデータを扱う際には、セキュリティやエラー処理など、他にも考慮すべき点がたくさんあることに注意してください。
To get the HTML to use the CSS and JavaScript, you need to link the CSS and JavaScript files to the HTML file using the `<link>` and `<script>` tags, respectively.

Here's an updated version of the HTML file that includes the links to the CSS and JavaScript files:

```html
<!DOCTYPE html>
<html>
  <head>
    <link rel="stylesheet" type="text/css" href="signup.css">
  </head>
  <body>
    <form id="signup-form">
      <!-- form content -->
    </form>

    <script src="signup.js"></script>
  </body>
</html>```

To record what users enter, you can use a server-side language like PHP, Node.js, or Ruby on Rails to store the form data in a database or as a file on the server. You can also use a web service like Google Forms, Wufoo, or Typeform to create and manage forms.

Here's an example of how you could handle the form data using PHP:

```php
<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
  $firstName = $_POST["first-name"];
  $lastName = $_POST["last-name"];
  $email = $_POST["email"];
  $phone = $_POST["phone"];
  $password = $_POST["password"];

  // Store the form data in a database or as a file
  // ...

  // Redirect the user to a thank you page
  header("Location: thank-you.html");
  exit;
}
?>```

And here's an updated version of the JavaScript file that submits the form data to the PHP script:

```javascript
const form = document.querySelector("#signup-form");
const passwordInput = document.querySelector("#password");
const passwordConfirmInput = document.querySelector("#password-confirm");

form.addEventListener("submit", (event) => {
  event.preventDefault();

  if (passwordInput.value !== passwordConfirmInput.value) {
    alert("Password and password confirmation do not match.");
    return;
  }

  form.action = "signup.php";
  form.method = "post";
  form.submit();
});```

Note that this is a basic example and there are many other considerations, such as security and error handling, when handling form data.