EmilyCarter1 Take security in consideration too, it's easy to fund a block of code that does what you want then then simply use it as is. Even tho it's full of security vulnerabilities. Check all input from
$_POST to ensure there's no shady stuff sent to the site.
Check file extension on uploaded files, say you allow upload of image files. Then you don't want a php file to be uploaded as it allows an attacker to take over your server.
Variables in PHP doesn't have strict data types, all of these 11 and '11' and "11" could be interpreted as number eleven. https://www.php.net/ has great documentation of every function and many good advices on how to use them properly.