Use case testing:- Use case testing is a high level functional black box testing technique which helps in determining/identifying test cases to test a particular system on a transaction by transaction basis from start to finish.
A use case is a description of interaction of an Actor(Actors are generally people/user) with a particular system in order to carry out a specific task. It is a sequence of steps of interaction, a Actor has with System. Use cases are defined in terms of actor not the system, describing what actor does and not on what a system accepts and its outputs.
Difference between Use case and Test case:-Use cases are High level test cases which describes all functionalities as per requirement whereas Test Cases are Low level requirements which describes the each step of the functionality, test data, actual result, expected result.
Lets take an ATM PIN example of Use case :- Here we will see successful and unsuccessful scenarios describing interaction between an actor and system. This is a simple ATM transaction process in which step 1 to step 5 shows success transaction and step 2a, 4a and 4b shows unsuccessful transaction.

Success Scenario (A: Actor, S: System)