how can i write text into a textbox and then press a button and save the text thats in the textbox to a file?

edit: i found this code:

http://www.tizag.com/phpT/filewrite.php

Code:
$myFile = "testFile.txt";
$fh = fopen($myFile, 'w') or die("can't open file");
$stringData = "Floppy Jalopy\n";
fwrite($fh, $stringData);
$stringData = "Pointy Pinto\n";
fwrite($fh, $stringData);
fclose($fh);
how can i make this code save from a textbox instead of a string?
... and make the linebreaks save with a <br/> tag?