The implementation of a “Tier Models” is a large part of an MVC framework. It represents the details of your application, and most applications are useless without data. Magento Models play an even greater role, because they usually contain the “Business Logic” that often (good or bad) are relegated to the controller helper methods or other PHP MVC frameworks.
The following is part of a longer series on Magento aimed at developers familiar with PHP MVC development. Although each article can be read stand alone, each article is based on concepts discussed in earlier articles. If you are confused, especially to catch up on the earlier work first.