@G-I-Jones As Scott mentioned, HTML would render the form for your users and you would use PHP to process that form to send the email. PHP won't send the actual email, you'll need a mail server to do this, but PHP will take care of getting the information from the HTML form and adding the necessary bits and data processing to forward off your email.
One caution though...are you sending personal, private information via email? If you are, you may want to rethink your approach or at least take steps to ensure that your browser connection to the web server is secure (Let's Encrypt can help here) and that you are sending the email from a TLS enabled email server to a TLS enabled email server otherwise your data is open to interception while in transit.
Definitely more than one way to skin this cat, depending on your full requirements.