1. Use case:
It will be developed by Business Analyst based on the requirement specification.
It is a detailed description of the Specification in a simplified version with realtime scenarios.
Based on Use case, test cases will be written by the testers.

2.Scenario:
While writing a test case for a module, you write different tests for that module say, Creating a user.
There may be several ways to create a user like, creating a user thru wizard or thru uploading set of users.
These are all the things we can call as a scenario. This is the literal meaning.

Test case:

What are all the steps we should follow for creating a user using a wizard and
What are all the steps we should follow for creating a user using upload are called as test case.