Set up a scheduled task to run a cronjob.php file on a server

Setting up a new ecard website and need some help with configuring a command for a php file as per instructions from the software developers. I don't have epanel as I'm on a shared host so need someone who knows how to set up a cronjob command manually.

Particularly interested in anyone who has worked on ecardmax systems before.

I will also need some ongoing help with customisation of the website template and css.