Hello,
Basically, you just need to implement the class with proper name and with a function create(&$uri). The function gets the nonSEF URL in $uri variable, you can do anything you want to transfer it to a nice SEF URL, and at the end you just need to call the JoomSEF::_sefGetLocation function, so the URL gets saved into the database.
Try following the code from our free extensions, it really is easy :)
Best regards,
ARTIO Support Team