require_once 'vendor/autoload.php'; $loader = new Composer\Autoload\ClassLoader(); // Register namespaces here $loader->addPsr4('Acme\\Demo\\', __DIR__.'/src'); // Register the loader $loader->register();In this example, we first require the autoload.php file generated by Composer, which initializes the Autoload class loader. We then create a new instance of the class, and use the `addPsr4()` method to register the Acme\Demo namespace, and specify the directory where our class files are located. Finally, we call the `register()` method, which tells the Autoload class loader to start looking for and loading the necessary class files. There are many packages available for PHP that can be installed and managed using Composer. Some popular examples include: - Slim (slim/slim): a lightweight PHP framework for building web applications - PHPUnit (phpunit/phpunit): a testing framework for PHP - Symfony (symfony/symfony): a full-stack framework for PHP web development By including these packages (libraries) in your PHP projects, you can leverage pre-built functionality and save time developing your own solutions from scratch.