Yeah if you have CPanel, or really any other control panel, it should be an option in there.
If not, the cron should look something like:
That assumes you want to run it at 12:00 AM.
0 0 * * * /home/username/script.php
To run it, you can make your script executable, and include the path to the PHP executable at the top like:
Or, you can change your cron command to call PHP directly:
or you can use wget if it is in the document root.
0 0 * * * php /home/username/script.php