Understanding and modifying a send email autoreply

With this email response to a form submission, I would like to include the info entered by the user in my autoreply to him. How do I do that?

Also, could you tell me the meaning of some things I don't understand?

What is the meaning of this line: "foreach($fields as $a => $b) ..."  Neither $a or $b have been mentioned yet in the code, so what do they represent? I can't find "=>" as a php operator, so what does it mean?  

In fact, so I can really understand how it works, what does each element in the whole line do:
foreach($fields as $a => $b){       
      $body .= sprintf("%20s: %s\n",$b,$_REQUEST[$a]); }

Thanks,
John

<?php 
$to = $_REQUEST['sendto'] ; 
$from = $_REQUEST['Email'] ; 
$name = $_REQUEST['Name'] ; 
$headers = "From: $from"; 
$subject = "Web Contact Data"; 
$fields = array(); 
$fields{"Name"} = "Name";
$fields{"Company"} = "Company"; 
$fields{"Email"} = "Email"; 
$fields{"Phone"} = "Phone"; 
$fields{"list"} = "Mailing List"; 
$fields{"Message"} = "Message"; 
$body = "We have received the following information:\n\n"; 
foreach($fields as $a => $b){ 	
	$body .= sprintf("%20s: %s\n",$b,$_REQUEST[$a]); } 

	
	$headers2 = "From: noreply@YourCompany.com"; 
	$subject2 = "Thank you for contacting us"; 	
	$autoreply = "Thank you for contacting us. Somebody will get back to you as soon as possible, usualy within 48 hours. If you have any more questions, please consult our website at www.oursite.com"; 
	
	
	if($from == '') {$ermsg = "You have not entered an email, please go back and try again";} 
	else { 
		if($name == '') {$ermsg = "You have not entered a name, please go back and try again";} 
		else { 
			$send = mail($to, $subject, $body, $headers); 
			$send2 = mail($from, $subject2, $autoreply, $headers2); 
			if($send) {header( "Location: http://www.discretedata.com/Test/thankyou.html" );} 
			else {$ermsg = "We encountered an error sending your mail, please notify me@mysite.com"; }
		} 
	} 
?>

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