What you want to do is create an HTML "Contact Us" page with a <form>
element, giving it a path and a method to your PHP page where you will handle all the information they put in, here is a tiny example to get you started
contactUs.html:
<form action="contactUs.php" method="POST">
<input type="text" name="username" />
<input type="password" name="userPassword" />
<input type="email" name="userEmail" />
</form>
contactUs.php:
<?php
$username = $_POST["userName"]; //We access the name attributes from our HTML form here
$password = $_POST["userPassword"];
$email = $_POST["userEmail"];
?>
And so forth, of course on your HTML page you want to style the form, and add any other information that you are asking from your visitor, and on your PHP page you want to add a "Thank you" message or some message that tells your visitor that their request was successful since it will redirect them away from your contactUs.html page and to your contactUs.php page, although there are ways of accomplishing the same task while staying on the same page.
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