PHP Scripts
PHP is a server based script programming language, which allows you to create dynamic websites. PHP has many advantages and is great to offer services like form mailers, guestbooks, counters or forums. Goldfish websites also can use PHP scripts. You can change the file suffix to ".php" in the preferences to include PHP scripts in html code items.
Some page items (e.g. the visitor counter) use PHP. All PHP scripts are stored in the support folder. There may be also a folder called "saved". That's the place where PHP scripts store their data (e.g. the visitor counter how many visitors where already on your website).
PHP And Your Webserver
Your webserver must support PHP, if you want to use PHP scripts. Otherwise your visitors will see the PHP code instead of the execution of the PHP Script. If you don't know something about PHP support of your webserver, ask your webhosting service.
Important if you use a third party FTP upload application: If your website contains a folder "saved", you must set the reading and writing permissions for owner, group and others to true. Otherwise the PHP scripts on your website will not work.
See the documentation of your php application, if you don't know how to change folder permissions on your webserver. Or use the built in FTP site publishing of Goldfish. It changes the permissions automatically.