An important part of the Unified Modeling Language (UML) is the facilities for drawing usecase diagrams. Use-cases are used during the analysis phase of a project to identify and partition system functionality. They separate the system into actors and use-cases. Actors represent roles that can are played by users of the system.
Those users can be humans, other computers, pieces of hardware, or even other software systems. The only criterion is that they must be external to the part of the system being partitioned into use-cases. They must supply stimuli to that part of the system, and the must receive outputs from it.
Use-cases represents the activities that actors perform with the help of your system in the pursuit of a goal. We need to define what those users (actors) need from the system. Use-case should reflect user needs and goals, and should be initiated by an actor. Business, actors, Customers participating in the business use-case should be connected to the use-case by association.