You should normally be able to run a php file (after a successful installation) just by running this command:
$ /path/to/php myfile.php // unix way
C:\php\php.exe myfile.php // windows way
You can read more about running PHP in CLI mode here.
It’s worth adding that PHP from version 5.4 onwards is able to run a web server on its own. You can do it by running this code in a folder which you want to serve the pages from:
$ php -S localhost:8000
You can read more about running a PHP in a Web Server mode here.