simply put, 

Test case is 2 + 2 = 4

and the Test Scenario is "addition"

Test cases are based on Test scenarios.

Test cases is concerned with a single functionality but where as test scenarios is concerned with end to end transaction with business point of view.
Test scenario is nothing but collection of test cases

enter a valid user name and valid password into corresponding 
fields into the login page and click on login button
.expected value is corresponding page should be displayed.



here Test scenario is clicking on "login" button ie performing 
some actions particular functional points

Test case is an idea of something doing on the Test Scenario