用例步骤和用例scenrios

I am modelling a system and i have the following are some of my use cases{appoint teacher(adimin),record grades(teacher), manage students(admin),record attendance(teacher), manage cocurricular(admin)} I have some problems with coming up with use case steps and use case scenarios. i have already drawn my conceptual class diagram. does any one have an idea on how to go about that?I am modelling a system and i have the followin