ruby beginner...

I have ruby 1.8.6 installed on windows. I want to view the doc
offline. I downloaded from ruby-docs.org a .tgz file which when
extracted was a 6-core-rdocs file. Not sure what to do with this. When
I run "gem server" and access the page i do not see the "core" and
"stdlib" documentation. How do I get these documentations ?

Thanks

gd