Interpret Code - Non PHP Programmer

What is this code doing?

<?php
if (!empty($_FILES)) {
    $tempFile = $_FILES['Filedata']['tmp_name'];
    $targetPath = $_SERVER['DOCUMENT_ROOT'] . $_REQUEST['folder'] . '/';
    $targetFile =  str_replace('//','/',$targetPath) . $_FILES['Filedata']['name'];

        move_uploaded_file($tempFile,$targetFile);
        echo str_replace($_SERVER['DOCUME开发者_Go百科NT_ROOT'],'',$targetFile);
}
?>

It is basically uploading a file and echoing the target file's name.

There should also be something like an HTML form to send the file to this script.

It accepts an user uploaded file, and puts it in your webroot in a folder, specified by the user. Then it outputs the path of the uploaded file.

This code is to upload a file in the destination directory. Is there anything else do you want to understand.

This will upload the file in the path you have in variable $_REQUEST['folder']

Storing files uploaded (possibly via HTML form) onto server.

It's accepting a file posted by a HTML form and uploading it to a certain directory within a server. After that it's displaying the location of the file on screen (in the browser).