sub on_msg {
     my ($self, $event) = @_;
     # $event contains all the interesting information,
     # for example $event->nick and $event->args
     $self->privmsg($event->nick, "You said " $event->args);
}
[download]

But you should note that Net::IRC doesn't seem to be actively maintained anymore (last version about 5 years old), nowadays most monks recommend POE::Component::IRC instead. If you want to write a simple bot, Bot::BasicBot really helps, it's much simpler to use.