There is no specific format for use case. Use case depends upon the situation and condition for a particular application. Use case is hard to understand by the user and the developer.it just gives an idea about each and every step for an application.The three main features of use case are.
Actor is a person which interact with the system for a particular goal. Actor is a stakeholder, means an actor can be a human or hardware or software, company or organization. An actor is a person who can make decision
A system is a collection of elements or components that are organized for a command purpose. In case of use case system interact with actor to achieve final goal.
Goal is the final output that an actor wants to have.
Basic structure of use case is:
1.Use case name
5.Flow of events.