I've installed https://github.com/pug-php/pug using composer and now I have a subdirectory vendor/pug-php/pug in my project but I can't figure out how to use it.
If I try
$pug = new Pug();
I obviously got
Class 'Pug' not found
How can I use it?
If you installed pug with composer you should find an autoloader.php in your vendor folder.
This made it work:
use Pug\Pug; include('vendor/autoload.php');
Take a look at the examples in pug:
This shows how you use it standalone.
The autoloader, which is missing in your question, you can find here: