Software testing is the process of reviewing a system or its component(s) to find if it completes the specified requirements or not. Testing is the process of executing a system in order to find any gaps, errors, or missing requirements in terms of the actual requirements. In testing, a Test Scenario is what to be tested and a Test Case is how to be tested. In other words, a test scenario is a group of test cases.
Test Scenario: This is used to test the end-to-end functionality of a software application and ensure the business processes and flows are functioning as per requirements. The tester thinks themselves as if end users and find real world scenarios (use-cases) that can be performed in testing. Once these test scenarios are completed, test cases can be written for every scenario. As Test scenarios are the concept of what to test.
Test Case: A test case is a collection of steps to be executed by the tester team in order to validate every scenario. A test scenario usually has multiple test cases related to it, as test cases layout the low-level details on how to test the scenario.