a usecase describes how a user can use a specific 
functionality

use case consists business logic

hhow to use a functionality

and user actions n system response

It is a functionality given by the user based on that we 
write the testcases.

Use case is description of user Actions and systems response
is called use case

The use cases are detailed design docoments than test cases.
It reduces the test engineer`s own assumptions. it mean TL 
provides these documents.Based on these we will create tset 
cases

Use case description is one of the alternative to SRS
document,if the Business requirements from a customer are
complex to understand then Out TL will prepare this Use case
document and he will give it to the Test Engineers to
prepare Test case.
In general following is the generally used Use case format
which consists of :
1)Use case id
2)Use case name
3)Use case Description
4)Pre conditions
5)Work Flow
6)Post conditions
7)Proto type model
8)Alternative work models

Regards
Preethi.G