At the download site, it says:
A small php script for cropping, zooming and resizing web images (jpg, png, gif). Perfect for use on blogs and other applications.
Developed for use in the WordPress theme Mimbo Pro, and since used in many other WordPress themes.
You can read more about the script, along with TimThumb tutorials, on the TimThumb Project Homepage
Grab the code from here: http://timthumb.googlecode.com/svn/trunk/timthumb.php
What am I supposed to do when I "grab the code"?