At the most basic level, PHP can do anything any other CGI program can do, such as collect form data, generate dynamic page content, or send and receive cookies.
Perhaps the strongest and most significant feature in PHP is its support for a wide range of databases. Writing a database-enabled web page is incredibly simple. The following databases are currently supported:
Adabas D InterBase Solid dBase mSQL Sybase Empress MySQL Velocis FilePro Oracle Unix dbm Informix PostgreSQL
PHP also has support for talking to other services using protocols such as IMAP, SNMP, NNTP, POP3, or even HTTP. You can also open raw network sockets and interact using other protocols.