Sending a confirmation email after registration

I have the code below to send an email to the registered user after completing a registration form
As a next step I would like to add a confirmation link that the user will receive in their email
(http://www.realestateonlinecy.com/regverificationaccount.php/hash=$hash)
the members table has the following fields
id, fname, lname, email, address, city, telephone1, telephone2, username, password, hash

How do I proceed? How do I generate a hash to store it in the database, and how should I implement the address for the verification to my code?

php 
error_reporting(E_ALL);

// SEND MAIL FROM A FORM

// A FUNCTION TO CLEAN UP THE DATA - AVOID BECOMING AN OPEN-RELAY FOR SPAM
function clean_string($str)
{
    $str = stripslashes($str);
    $str = trim(preg_replace("/ +/", " ", $str));
    $str = preg_replace('/^ a-zA-Z0-9&+:?_\.\-/', '', $str);
    return $str;
}


// IF THE DATA HAS BEEN POSTED
if (isset($_POST['email']) && !empty($_POST['email']))
{
	// REQUIRED VALUES ARE PREPOPULATED - CHANGE THESE FOR YOUR TEST
	$to  = clean_string($_POST['email']);
	$from  = "noreply@realestateonlinecy.com";
	$subj  = "RealEstateOnline Registration";

	// CLEAN UP THE POTENTIALLY BAD AND DANGEROUS DATA
	$fname         = clean_string($_POST["fname"]);
	$lname         = clean_string($_POST["lname"]);
	$email         = clean_string($_POST["email"]);
	$address       = clean_string($_POST["address"]);
	$city          = clean_string($_POST["city"]);
	$telephone1    = clean_string($_POST["telephone1"]);
	$telephone2    = clean_string($_POST["telephone2"]);
	$username      = clean_string($_POST["username"]);
	$password1     = clean_string($_POST["password1"]);
	$password2     = clean_string($_POST["password2"]);

	// CONSTRUCT THE MESSAGE
	$content ='';
	$content   .= "Dear $fname $lname,\n\n";
	$content   .= "We would like to welcome you to our member zone\n";
	$content   .= "and thank you for registering to our website\n\n";
	$content   .= "With Regards\n\n";
	$content   .= "Real Estate Online";
	$content   .= "Member Services\n\n";
        
    mail( $to, $subj, $content, "To:$to\r\nFrom: $from\r\n");


	// To Admin
	$to1    = "admin@realestateonlinecy.com";
    $from1  = "noreply@realestateonlinecy.com";
	$subj1  = "RealEstateOnline - Member Registration";

	// CONSTRUCT THE MESSAGE
	$message    = '';
	$message    = "This is an automated message to let you know that\n";
	$message   .= "there is a new registration on the Real Estate Website from $fname $lname\n\n";

	// SEND MAIL
    mail( $to1, $subj1, $message, "To:$to1\r\nFrom: $from1\r\n");

}
?>

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