Actually, the snippet makes a lot of sense when you know it's PHP. The $_FILES superglobal is created when a form element to a submitted PHP page contains a file upload. The translation of:

$tmp_file_name = $_FILES['Filedata']['tmp_name'];
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is "Retrieve the temporary file name PHP created (the tmp_name) of the form element Filedata and put it in the string tmp_file_name

The next line:

$ok = move_uploaded_file($tmp_file_name, '/path_to/new_filename');
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makes use of the PHP move_uploaded_file function (hence the OP can't show the source - you're asking for PHP's own source). That function takes the uploaded file and moves it to a directory specified by the second parameter.

The Perl way to do this is best outlined (as Anonymous Monk already posted) in CGI - Processing a File Upload Field. The field name is Filedata, and from that you should be able to determine the rest.