How can I send an automatic email on a certain hour

I would like to know how could I send to all the pepole who registered
to my website an email at specific date/hour automaticlly without needing
me to log and press send.

How can I do that?

Set up a cron job to run the PHP script for you.

Oh thanks.
I seached about it a liitle bit in google and only found ways to set the date from the Control Panel (CPanel).
What if I want to change it / add more tasks without needing to go to the control panel (CPanel) evry time?
Is there a way to add a new task to the Cron Job using php functions?

If your functions are to be used every hour then you can include them within the same php file for the cron job.