Login and register problem php

Hello who help me pls…

here is error from my website who fix me error pls

Fatal error: Uncaught Error: Call to undefined function mysql_connect() in /srv/disk5/2843464/www/fkdubnica.atwebpages.com/LoginAndRegister/register.php:7 Stack trace: #0 {main} thrown in /srv/disk5/2843464/www/fkdubnica.atwebpages.com/LoginAndRegister/register.php on line 7

How is this Unity related?

i create in unity login and register but error is on website pls help me