I didnt understand the how work pathtovars, a php gpl script

Hello, I was looking for a query_string wrapper for web crawlers I found pathtovars : http://www.phpclasses.org/browse.html/package/561.html English is not my native language. I didnt manage to use efficently this script ! Even with the sample ! I don't know how to map url ? How to generate an url ? How to retrieve variables values in the current url ? I found this script with a very little doc. Is there someone that can have a look and try to explain me simply ? For eg : How to retieve : $var1 = value1 $var2 = value2 with that on that script http://www.domain.com/var1_value1/var2_value2/ .... Thanks.