From Achievo/ATK Wiki

Intro

In this lesson you can see a complete application to add, edit, view and delete employees from a table, as well as search for employees by name, select all employees whose names start with a given letter and calcualte the total salary of all the employees put together.

All of this is done in two source files with a surprisingly small number of lines.

The Employees Node

The file class.employee.inc contains the definition of a node. It describes what fields the node contains, and hints for the user interface of the admin screens. You should read through the well-documented code in this source file (available by clicking "View the source for this node" at the bottom of the Employee - Administration window) to learn how to create a node.

The Module

The file module.inc contains the definition of the lesson1 module. For our purposes, you can think of the Module file as the place where the application menu is defined. Select "Module Source" from the lesson 1 menu and read through the well-documented code to learn how to create a menu.