Use Case Testing is a functional black box testing technique that helps testers to identify test scenarios that exercise the whole system on each transaction basis from start to finish.
Use Cases capture the interactions between 'actors' and the 'system'.
'Actors' represents user and their interactions that each user takes part into.
Test cases based on use cases and are referred as scenarios.
Capability to identify gaps in the system which would not be found by testing individual components in isolation.
Very effective in defining the scope of acceptance tests.
The Below example clearly shows the interaction between users and possible actions.