I'm new to both ruby and rails (coming from an experienced background in PHP) and I am attempting to create a webapp with rails. I need to have a user class manage users by authenticating, creating, updating, etc. and this class will be used on many pages/controllers with rails.

Where would be the best place to store this class file? What would be the best way to include it within a page? How can I allow the class to use other Rails classes (activerecord)?