Test Scenario and Test Case

i. Test Scenario is the high-level description of the functionality/ feature.
ii. It tells what to test in an application.
iii. Test Scenarios are derived from the SRS (Software Requirement Specifications)/BRS (Business Requirement Specifications) document.

Example:
In an Online Shopping Application, login functionality is one of the feature. We write test scenario as:
Test Scenario: Test the Login Functionality

i. Testcase is the detailed description of a functionality, which includes id, title, preconditions, test steps, test data and result.
ii. It tells how to test a functionality.
iii. Testcase is derived from the Test Scenario.

Example:
In an Online Shopping Application, the test scenario is login functionality. The test cases can be written as:
Testcase 1: Verify the user is able to login with valid credentials
Testcase 2: Verify the user is unable to login with invalid credentials