- Create your module (MyModule). It must be installed using module manager.
- Just copy plugins/function.news.php to plugins/function.mymodule.php (do not use exactly the same name, to use small letters wil be ok
- Change name of those 3 funtions according with your name, for ie:
function smarty_cms_function_mymodule(…
function smarty_cms_help_function_mymodule(..
function smarty_cms_about_function_mymodule(..

- Change content of the last one as well.

You must see this plugin in Tag area (admin)

To call it in page/template write mymodule in between big brackets like any other plugin.