Action Pack splits the response to a web request into a controller
part (performing the logic) and a view part (rendering a template).
This two-step approach is known as an action, which will normally
create, read, update, or delete (CRUD for short) some sort of model
part (often backed by a database) before choosing either to render a
template or redirecting to another action.

Action Pack implements these actions as public methods on Action
Controllers and uses Action Views to implement the template rendering.
Action Controllers are then responsible for handling all the actions
relating to a certain part of an application.  This grouping usually
consists of actions for lists and for CRUDs revolving around a single
(or a few) model objects.  So ContactController would be responsible
for listing contacts, creating, deleting, and updating contacts.  A
WeblogController could be responsible for both posts and comments.

Action View templates are written using embedded Ruby in tags mingled
in with the HTML.  To avoid cluttering the templates with code, a
bunch of helper classes provide common behavior for forms, dates, and
strings.  And it's easy to add specific helpers to keep the separation
as the application evolves.