You won't even notice it. Everything you already have will continue to work fine. All you have to do is include the autoloader somewhere in your code path. An

You won't even notice it. Everything you already have will continue to work fine. All you have to do is include the autoloader somewhere in your code path. An example assuming you already installed composer on the machine into your /bin or similar directory. # add a new dependency: composer require guzzlehttp/guzzle # this dependency will now be in the vendor directory ls ./vendor # update your apps entry point (ie: frontcontroller.php): // require composer's autoloader require ('vendor/autoload.php'); # autoload will now find any dependencies you add via composer // create guzzle client $client = new \GuzzleHttp\Client(); # another tip, if you already have a bunch of class files some where (ie: myapp/src/classes , myapp/src/models ) You can include class paths via composer.json "autoload": { "classmap": ["classes/", "models/", "MyClass.php"] } You can now remove any hard-coded include or require statements. There is a lot more things you can do with it but this is the most basic example.