Setting up model for existing database

I thought I sent this email (below) to the rails list, but can see no
trace of it today! Apologies if it did indeed appear yesterday…

I have an existing database (Microsoft SQL). I know how to specify the
connection to the database, but how can I generate or write a model that
correpsonds to a table or tables that already exist in the database?
Just by specifying things in a new model that match up to the database?
Has anyone got a pertinent example?