CGI with rails...

I'm a newbie to rails and programming...
I don't know anything about CGI scripts... The only thing I know about
CGI is that it stands for Common Gateway Interface. To be honest with
you, this is as concrete as it gets!!!!! Please someone help me with
that so at least I understand what it is, concretely, and that I can
use it if I need to. If you guys have examples (code) that might help
as well.

Thank you