Not sure if I understood the use/purpose of PHP entirely, but what seems to me that a .php file only executes when it is being called/executed by something before it, could be a html or a php file.
A thought, is it possible that a php file written, and it would just be activated by its own, example over a duration span of time, every week or so it would do something?
Thanks for looking...
You are looking for a cron job. This allows you to save a line of code on your remote server that will execute based on the criteria you set. You can make it execute a variety of files but PHP files are definitely one of the files you can execute in this manner.
As mentioned by nathan, you will be looking for a cron job. This is a server side setting in the server that will call a url at a set interval.
You seem to not really understand how PHP works. PHP scripts are called server-side before sending data to the client. They are run once when the client is accessing the script.