Lifecycle
Many objects in the system have predefined lifecycles whose rules are governed by the base-package and cannot be changed. For example, a service agreement starts out in the Pending Start state and eventually becomes Closed when it's been final billed (and paid). You can't change the system to allow a service agreement to starts its life in the Closed state.
The lifecycle of cases is not governed by the base package. Rather, you define the lifecycle of your cases when you set up their case types. Examine the following diagrams; the one on the left shows the potential lifecycle of a case that manages a high-bill complaint, the one on the right shows the potential lifecycle of a case that manages a customer's literature request.
Potential Lifecycles Of Two Types Of Cases
Note: 
Just examples. The above lifecycles are just examples. When you set up your case types, you must define the valid states for your case type.
The topics that follow describe important concepts that are illustrated in the above diagrams.