<?php
// File: src/Payment/Stripe/Client.php
namespace App\Payment\Stripe;

class Client
{
    public function charge(float $amount): Receipt { /* ... */ }
}

<?php
// File: src/Http/Client.php
namespace App\Http;

class Client
{
    public function get(string $url): Response { /* ... */ }
}

<?php
namespace App\Service;

// Import with 'use'
use App\Payment\Stripe\Client as StripeClient;
use App\Http\Client as HttpClient;
use App\Entity\{User, Order, Product};  // Group imports

class PaymentService
{
    public function __construct(
        private StripeClient $stripe,
        private HttpClient $http,
    ) {}
}

<?php
// Manual autoloading (don't do this in practice)
spl_autoload_register(function (string $class): void {
    $path = __DIR__ . '/src/' . str_replace('\\', '/', $class) . '.php';
    if (file_exists($path)) {
        require $path;
    }
});

composer init

{
    "name": "acme/my-project",
    "description": "My PHP project",
    "type": "project",
    "require": {
        "php": ">=8.2",
        "guzzlehttp/guzzle": "^7.8",
        "monolog/monolog": "^3.5"
    },
    "require-dev": {
        "phpunit/phpunit": "^11.0",
        "phpstan/phpstan": "^1.10"
    },
    "autoload": {
        "psr-4": {
            "App\\": "src/"
        }
    },
    "autoload-dev": {
        "psr-4": {
            "App\\Tests\\": "tests/"
        }
    }
}

composer install              # Install dependencies from lock file
composer update              # Update dependencies to latest matching versions
composer require vendor/pkg  # Add a dependency
composer require --dev vendor/pkg  # Add a dev dependency
composer dump-autoload       # Regenerate autoload files
composer dump-autoload -o    # Optimized (classmap) for production

<?php
// This single line loads everything
require __DIR__ . '/vendor/autoload.php';

// Now all classes from your project (App\*) and dependencies are available
$client = new \GuzzleHttp\Client();
$logger = new \Monolog\Logger('app');