You put the action coding inside feedback.php. First you get the form parameters using for example:
$name = $_POST["name"];
etc...
Where the name inside the $_POST is the name you gave to the input tag in your form.
You can then program as necessary to either e-mail it to yourself (using the PHP mail function for example) or save it on a database.
Not sure how much you know about PHP but the place to start learning is:
PHP Tutorial
and if you are already familiar with some programming in PHP, full details of the language can be found at:
PHP: PHP Manual - Manual