use XML::Twig; # maybe you forgot the semi column at the end of the line ;--)

Slightly more seriously, reading the aptly named README file in the distribution and following the links it gives would be a good start. perldoc XML::Twig, or getting the same docs through Activestate's doc browser (I believe there is such a beast) will also give you the reference doc, and starts with a pointer to the same places.