Some instructions for this script state: "Place in ~/.vim/indent/ and let 'er rip!"
This may be cryptic to some users. To elaborate a bit...
The script specifically redefines "indentexpr" to be a new function "SuperShIndent()".
After the script is in that directory, when you are running Vim you can ":source ~/.vim/indent/sh.vim" to cause the redefinition. Thereafter, any time you use indentexpr, you will be using the new function.
To learn about indentexpr, run Vim and execute ":help indentexpr". --January 6, 2012