Du.html simply prints out the total size in kilobytes and megabytes of html files, specifically those in the current directory and all subdirectories. It only works in summary mode.
Du.html requires some standard linux utilities like find and cut as well as perl. You can get the program here: du.html. Save it to disk somewhere in your executiona path (to find out what that is type echo $PATH. Then make it executable (chmod +x /full/path/to/file). Then just try it out. For example when I run it in my Linux the Universe and Everything directory I get the output:
There are 135 kilobytes or 0.1 megabytes of HTML files