loginregister: Fatal error: Uncaught Error: Class 'PhpMailer' not found

I just copy-pasted the whole project , what is the problem?

Fatal error: Uncaught Error: Class 'PhpMailer' not found in H:\xamp\htdocs\loginregister-master\classes\phpmailer\mail.php:3 Stack trace: #0 H:\xamp\htdocs\loginregister-master\includes\config.php(34): include() #1 H:\xamp\htdocs\loginregister-master\index.php(2): require('H:\\xamp\\htdocs\\...') #2 {main} thrown in H:\xamp\htdocs\loginregister-master\classes\phpmailer\mail.php on line 3