Tasks cannot be completed without resources. Resources are the people, equipment, and material needed to complete a project. When you assign a resource to a task, Project 2003 looks at the resource's cost and availability. Cost refers to how much money a resource will require. Availability establishes when a resource can work on a task and for how long. Project does a terrific job of managing the resources assigned to tasks.
Assigning resources to tasks helps to keep things organized in the project. For example, you don't want to accidentally schedule a task to be done when a resource isn't available or forget to find someone to complete a certain task. Setting up resources is especially worthwhile if you have time or money constraints for your project. If you don't enter resource information, Project calculates the time and scope of the project, but you will have no idea how much cost is going into the project.