Newb here coming from C++

Ok, I _think_ I know what a class variable is.  It is similar to a
static variable in a class in C++.  Rght?

An instance variable is apart of an instantiated class, right?

What's a singleton?  I don't think it's the same as as singleton in
C++ parlance.

- - -

If Class X wants to access a class variable and/or constant in Class Y, must a class
method be defined or is there a direct way to do it?

Besides the Pickaxe book, can anyone recommend a document that
describes this a bit more clearly?

- - -

So I did a search for "ruby for c++ programmers." on Google and came
up with exactly one article
(http://californickation.blogspot.com/2008/02/first-look-at-ruby.html)
... one that says "Another funny fact is that searching for "Ruby for
Java programmers" retrieves a few articles right on the first page while "Ruby for C++ programmers" does not."

Anyone know of any articles?