1.Objective
2.Prerequisite
3.Verify

For wirttin scenario the four steps is

      Scenario contains three attributes

one is scenario id
second one is scenario description
third one is priority

    the four steps is 
           1) Identify each scenario with unique id, that 
is scenario id must be unique.
           2) Always scenario description starts with a 
verb , Avoid adjectives in description.
           3) As and when u write scenarios , assign a 
priority to it.
           4) Divide the application to functional module 
s , and write scenarios for the module.