It's not a matter of me being unhelpful. It's a matter of you coming to a forum and asking a question, one that is ambiguous at best. Then when we try to get more information about what it is you're working on/with, you give us no information which shows your infancy inside of working with PHP.
You can't have PHP 7.x since right now the most recent build is only 5.x. You say you have an application and change things in the Preferences, but make no mention of exactly what application/script you're using.
How can we help when the information you're giving us is not there? What you need is either a book to teach you the basics, OR a personal tutor on which no-one here can do that for you. It's impossible. I've answered your question in an above post. You send mail using [man]mail/man in a PHP file. Since you say you're supposed to get an email and such, I'm guessing you're using a CMS and haven't set it up properly; however, if you don't tell us what you're using, or where your website is, we can't help you any further.