Email when closing a case

Hi. I've set up a web-to-case form and installed it on my website.

When I answer and resolve a case and close it, is it possible to have an automated email go back to the creator of the case, the person who sent it to advise them it's closed?

I know how to make the email but I don't know how to automate it.

Also, what will be the trigger? Do I just enter the date closed? or do I change the status to closed? or do I need to do both?

Thanks