eRuby Fastcgi lighttpd deadend

I have been trying to work out how to use eruby and fastcgi but it’s not
an easy process. All the websites out there focus on rails and the ruby
fastcgi library documentation is nonexistent.
So far all I know for sure is I need to make a persistent ruby script.
Name it something like dispatch.rb. Put that as the fastcgi binary in
the lighttpd setting then use that script to forward input to the ruby
pages for my site.

I was wondering in anyone knows of any tutorial for this or what I
should read. Should I be trying to gain a better understanding of
fastcgi or the ruby fastcgi library? In simple terms I don’t even know
where to start.

I have made sites using eruby and the cgi standard library and found it
very simple.

Normally I would never post something so trivial but I am totally stuck.