Composer autoloading of custom classes and files explained

You might know already now to pull in dependencies via composer and that you just need to include vendor\autoloader.php composer file in order to load all the classes that you pulled as your dependencies. But what happens when you want to use your own custom classes and also use composers magical autoloading and not only plain old php style of including each and every class and file that you require for your application to work? Composer makes this extremely easy and allows you to easily autoload your custom classes, namespaced classes and php files.