Executing php with crontab

I’m trying to run a php-script on a scheduled basis. So I’d thought crontab was a good idea. The server I’m using is on Linux which I’m not that familiar with. So the problem I’m having is, I don’t know how make the script executable from php. I need to reference the script, or put it into a folder that can run php from the command line. So I don’t know what path to give my crontab, for example: