Rails 3 Observer -- looking to learn how to implement an Observer for multiple models

I'd like to add an Auditor Observer which does an action anytime after_create for 3 models (books, characters, authors)...

I recently heard of the Observer capability but can't find any documentation on the ability. Is it support in Rails 3?

How do I create an Auditor Observer that does something after_create for 3 models?

Thanks