How do i upload files for my website for download.

If you link to the PDF then when anyone clicks on it, it will open the PDF and they won't actually download it unless they save it when it is open.
Robert Plank put this code in the main forum last year that will make the PDF downloadable.

<?php

// Change this to the filename of your PDF file
$filename = "filename.pdf";

if (!file_exists($filename)) {
header("HTTP/1.0 404 Not Found");
echo "<h1>404 Not Found</h1>";
die();
}

header('Content-type: application/pdf');
header('Content-Disposition: attachment; filename="' . basename($filename) . '"');
echo file_get_contents($filename);
die();

?>

Change the filename that's underlined above to the name of your PDF.
Copy the code to to a blank file in wordpad or what ever text editor you use and name it what ever you want with a .php extension, like ebook.php
Upload that and the PDF to your site and on the web page link to that file like this http://sitename.com/ebook.php
Then when they click on the link it will download to their computer instead of opening in their browser.