Rb_const_get documentation

What's the best place to find out more about the rb_const_get family of functions for writing C extensions? I'm writing my first C library for Ruby, and struggling with how to get VALUEs for Classes and Modules provided by Ruby and other extensions. The Pickaxe 2.0 has a wonderful section on C extensions, for the most part, but it seems to omit mention of rb_const_get completely. Took me an hour of searching the ml to even discover its existence.

A few pressing questions:
(1) What does the rb_cObject parameter that I'm always passing in do? What other things might I pass in for this argument?
(2) How do I get a handle to a Class that's inside a module? I tried calling (for example) rb_const_get(rc_cObject, rb_intern("GLIT::Vec")) but I get an error. However, calling GLIT::Vec.new from a ruby script that's using the C extension works fine, so I must have the syntax wrong.

Thanks a bundle for any help you all can provide. I appreciate it.

-- Brian Palmer