How can I use Stripe API Reference PHP?

Hello,

I would like to check something with my custom function.

Is it possible to use e.g.:

$stripe = new \Stripe\StripeClient(
  'sk_your_key'
);
$stripe->sources->retrieve(
  'src_1JnChv2eZvKYlo2CGbRagYAZ',
  []
);

It is from here:
https://stripe.com/docs/api/sources/retrieve?lang=php#retrieve_source

If yes then how? Because when I try to do it then I get Fatall error:
‘ PHP Fatal error: Uncaught Error: Class ‘Stripe\StripeClient’ not found’

Thank you in advance for help.