Form action parameter opening php script

My problem is relatively simple, I have a form and I need it: by clicking the submit button the data is passed to a php file (referenced in the form's action parameter) that will save the data in a database. However when I click the submit button the form displays the code from my php file (I am using an external file for php). The expected result would be that nothing would be displayed and the data would be saved in the database, how do I do that?