How does Composer work in relation to PHP development, and what steps are necessary to deploy PHPMailer on a server for production use?

Composer is a dependency manager for PHP that allows you to easily manage and install libraries and packages for your PHP projects. To deploy PHPMailer on a server for production use, you need to first create a `composer.json` file in your project directory, add the PHPMailer dependency, run `composer install` to install PHPMailer, and then include the PHPMailer autoloader in your PHP script.

// composer.json
{
    "require": {
        "phpmailer/phpmailer": "^6.5"
    }
}
```

After creating the `composer.json` file, run the following command in your terminal:

```bash
composer install
```

Then, in your PHP script, include the PHPMailer autoloader:

```php
require 'vendor/autoload.php';

// Now you can use PHPMailer in your script
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\SMTP;
use PHPMailer\PHPMailer\Exception;