You begin a development project by first identifying its users, the goals that the user wants to achieve, or a particular problem to be solved, and then discovering the functionality and environment of the system that will achieve these goals or solve the problem. You gather information about, and document, the functional requirements, and identify which requirements are associated with specific functions, tasks, or behaviors of the system. When you have identified the requirements, you can create a use case model to describe the functionality in terms of how the system will be used.