You mean an active record model class?
There are literally hundreds of examples from tutorials all over the
web. You will need to have a basic grasp of Object Oriented
programming concepts like classes, encapsulation, etc.
Have a look here:
It gives enough example of models to get you started.
(Hint: It is the part that starts "class Product < ActiveRecord::Base")
M. R. :
No, I don't mean the topic "active record model class". I've some
different model classes in my rails-project. Now, I would like to draw a
picture of my design - it's calling design model. These design model is
a image, that explain, how the different classes are arranged in the
model and which relationships they have to the other model classes. Draw
a design model is a step in the software engineering process.
That is incredibly cool. It also saves me the trouble of teaching SQL
Fairy about Rails conventions =)