I see you have a script to process the form submission. That's good.
But you still need the form.
This is an excellent site to learn how to code forms: http://www.w3schools.com/html/html_forms.asp
And this, if you just need a simple form quickly, can help you generate form code: http://www.willmaster.com/create-form/
Use the PHP script as clues for naming the form fields. Form field name="senderName" for the name of the person filling in the form, for example.
I wish you the best. Coding can be a pleasure.