Codecademy’s course on PHP does not teach you PDO’s (PHP Data Objects), PDO’s are used to connect and interact with databases, before PDO’s one used functions like mysql_query();
These functions no longer work and are probably deprecated, meaning if you also want to learn how to provide form data to a database or a script then learn PDO’s, there are tutorials on YouTube, I recommend watching one from this year.
EDIT: PDO’s are the only way to connect and interact with databases if you are using PHP 7 or above. If you’re using a previous version the functions may work (depends on the version of PHP you’re using).
NOTE: This post has nothing to do with Advanced Arrays whatsoever, it’s just a tip given that after I completed their course I wanted to learn how to connect and interact with databases and Codecademy didn’t provide information on that, and I then struggled due to watching an abundance outdated tutorials using deprecated code, hence I’m trying to help others avoid wasting time and energy trying to figure out why their code won’t work.